When two jets or streams of water moving with equal or unequal velocities meet at an angle and combine to form one common stream, the impact is usually accompanied by loss of energy, which may be large if the velocities are high. If the jets are free (exposed to air on every side), the pressures are unaltered by impact, and the loss may be readily calculated in terms of the initial velocities and angle of inclination, by an application of the equations of energy and of momentum. Where the streams are confined before and after impact—as, for example, where the streams outflowing from the impeller of a centrifugal pump impinge on the more slowly moving body of water in the volute, or where the two streams combine in the mixing chamber of a jet pump or injector,—both pressures and velocities are altered by the impact, and the available data are insufficient to enable the magnitude of the losses to be predetermined from a priori reasoning.

During the past few years probably no group of fossil plants has received more attention from palæobotanists than that of the Pteridospermeæ. Many fern-like impressions, derived from Carboniferous rocks, have proved to be members of this division of the vegetable kingdom; while many more may ultimately be removed from the Filicales and included in the Pteridospermeæ. Specimens, however, in which the internal structure is preserved, may, as a rule, be correctly referred to their respective class, but among those included in the latter group there is considerable diversity of organisation, and recently described genera have tended to increase the diversity of type rather than to indicate relationships among the forms already known.

The material placed at my disposal for the purposes of this paper comprised the brains of four adult specimens of the Weddell seal, in addition to the brain of the young animal which has formed the subject of my former contributions. The four adult brains having been removed at the time the animals were killed, and preserved in a solution composed of spirit (90 per cent.) 6 pints and formal (2 per cent.) 4 pints, were, with one exception, in a firm and satisfactory condition for detailed anatomical examination. The body of the young seal had been preserved with a view to ordinary dissection, and therefore its brain was not in the firm state of the adult specimens; but as I had the opportunity of removing this brain from the skull, I was able to observe the disposition of the dura mater to the hemispheres of the cerebrum and cerebellum. While the dura mater presented, as a whole, its usual arrangements, it was noteworthy that the falx cerebri did not act as a septum between the two hemispheres of the cerebrum except to a very slight extent, and certainly for not more than one-third of the distance between the vertex of the cerebrum and the dorsal surface of the corpus callosum. As a result, in the region referred to the opposing mesial surfaces of the two hemispheres lay not only in close apposition with each other, but their convolutions were intimately adapted to each other. Similarly, the tentorium cerebelli only extended a short distance between the cerebrum and the cerebellum, and, as the occipital ends of the cerebral hemispheres fell considerably apart from each other, there was space for the accommodation of the well-developed vermis of the cerebellum as well as for the bulbous pineal body, which occupied a position upon its dorsal aspect. As I removed the brain from the skull the stalk of the pineal body gave way, and probably the same thing had occurred during the removal of the adult brains, for, while different lengths of the stalks had been preserved, there was only one complete specimen of its bulbous extremity. Looked at from the vertex, the general outline of the whole brain was that of a four-sided figure with rounded angles, and the cerebral hemispheres concealed the cerebellum except where the vermis was exposed between them at their occipital ends. The frontal ends of the hemispheres were not rounded into frontal poles; but, on the contrary, they almost formed flat frontal surfaces. Similarly, the occipital ends were rounded and not pointed to form occipital poles. There was a small amount of difference in the absolute size of the adult brains, and the largest specimen measured 120 mm. in its fronto-occipital diameter ; 115 mm. in its greatest transverse diameter at a point well forward on the temporo-sphenoidal lobes; and 71 mm. in vertical height, measured from the pons varolii to the vertex of the cerebrum. Thus, apart from the peculiarity of its general outline in total size, it was only slightly less than an average human brain. Throughout the anterior two-thirds of their extent the cerebral hemispheres were, as already indicated, in very close apposition, and the falx cerebri only dipped into the pallial or superior longitudinal fissure to a slight extent; but in its posterior third this cleft opened to form a wide interval, measuring 65 mm. in the transverse direction at its hinder end and narrowing as it ran forwards towards the posterior end of the corpus callosum. In the deep level of this interval the pineal body and the upper surface of the vermis were visible, as well as part of the upper surface of the cerebellar hemispheres. It should be stated that the backward extension of the occipital lobes of the cerebrum carried them 2 mm. beyond the cerebellar hemispheres.

In its essential features the basal aspect of the brain conformed to current descriptions of the mammalian brain ; but it presented many special points of interest, to which reference will be made in the course of my survey.

The specimens submitted for examination were:

(a) Portions of the brain (labelled Specimen XXXI.).

(b) Portions of spinal cord (labelled Specimen XXIV.).

Both were in excellent condition as regards fixation and hardening, having been preserved for many years in a fluid composed of formol and 95 per cent. alcohol (the fluid was also injected into the cerebral vessels). They were, previous to histological examination, submitted to the following processes:—

i. Comparatively thin slices were taken from various regions and placed for twenty-four hours in absolute alcohol.

ii. Then transferred to acetone for twelve hours.

iii. Placed in xylol until permeated.

iv. Embedded in paraffin of melting-point 52° C. Sections were then taken with an improved form of the Cambridge rocking microtome, and fixed to slides by means of the albumen method.

In an account of the Jurassic flora of Sutherland, published in 1911, it was stated that a few petrified specimens from Eathie Bay, Cromarty, and from Helmsdale on the coast of Sutherland, would be dealt with in a subsequent paper. One of the best preserved of them forms the subject of a recent communication to the Royal Society of London. The majority of the specimens described in the following pages are from the Hugh Miller collection in the Royal Scottish Museum, Edinburgh. We take this opportunity of expressing our thanks to the Director of the Museum for the loan of the fossils, and for permission to have sections prepared for microscopical examination. For the loan of the section reproduced in Plate II. fig. 19 we are indebted to the generosity of Dr Kidston.

From the thirteenth to the seventeenth century a successful whale fishery was prosecuted in the Bay of Biscay and in the North Atlantic by seamen from the Basque ports of France and the north of Spain. So daring was their enterprise that they pursued their avocation northward to Iceland and even westward to Newfoundland and the adjoining shores of the American continent. The reputation of the Basque sailors as skilful whaling fishermen was so widely recognised that, when the whaling companies in England and Holland were started in the early years of the seventeenth century, Biscayan seamen were employed as the harpooners to strike the whales, and as coopers to construct the casks to contain the blubber. Up to that time the knowledge of the specific differences amongst the large whalebone whales was most imperfect, and it is not unlikely that both Right Whales and Fin Whales were captured as opportunity offered, though the former, from the greater length of whalebone and the thickness of blubber, were more prized. In 1611 an English whaling company sent for the first time an expedition to Spitzbergen, and from the instructions given to its commander, Thomas Edge, it would seem that two kinds of Right Whales had even then been noticed, the one larger and more valuable from the oil which it yielded and the length of the baleen, now known as the Greenland Right Whale, Balæna mysticetus, and the other a smaller whale, called the “Sarda.” A whale captured off the coast of Iceland by the French and Spanish seamen, locally named “Sletbag,” was probably the same as the Right Whale the “Sarda.” With the development of the whale fishery in the Arctic Ocean, it became more evident that the Greenland Right Whale was distinct from the smaller animal which had previously been the object of pursuit. In 1671 F. Martens gave the name “Nordcaper” to Baleen Whales captured near the North Cape ; they differed from those which frequented the Spitzbergen seas in being smaller, with less blubber, shorter whalebone, more active and more dangerous to kill. The name Nordcaper continued to be employed as equivalent to the Baleine de Sarde of the French naturalists, and Bonnaterre and Lacépède, adopting nordcaper as a specific name, distinguished it from Balæna mysticetus, La Baleine tranche, or the Greenland Right Whale.

In 1804, Lieutenant-Colonel Imrie communicated to the Royal Society of Edinburgh a paper entitled “A Description of the Strata which occur in ascending order from the Plains of Kincardineshire to the Summit of Mount Battoc, one of the most elevated points in the Eastern District of the Grampian Mountains.” He pointed out that, in a short stretch of six miles in the North Esk section, “we pass from the secondary horizontal strata of the newest formation to the vertical, contorted primary strata of the oldest date, and terminate with granite, the primitive rock in the conception of many geologists.”