468 



NATURE 



\Apru 16, 1874 



tened out from above downwards, but are still separate, 

 and the lower-jaw arch, besides being divided into paleto- 

 quadrate and Meckel's cartilage, has approached still 

 more nearly to the adult character by the conversion into 

 fibrous tissue of its apex (Figs. 2 and 3, M Pt). 



The third stage described was a ripe embryo, about two 

 inches long, having nearly the form of the adult. In this 

 condition the external gills have entirely disappeared, the 

 internal gills now performing the whole function of respi- 

 ration. The skull has assumed all the characters of the 

 adult, except as regards a few minor details, chondrifica- 

 tion and segmentation being perfect. The investing mass 

 has not only completely enclosed the notochord, but has 

 formed an arch, like that of a vertebra, over the hinder 

 part of the brain : in this way the occipital region of the 

 skull is formed. The roof and walls of the brain-case, 

 membranous in the last stage, have now become carti- 

 laginous, and are fused with the nasal sacs in front, the 

 trabecuhi; below, and the auditory capsules and occipital 

 region behind. The trabecute form the whole of the 

 flat skull-floor in front of the ear capsules, where their 

 original apices (pharyngo-trabeculars) are still to be seen 

 as small rounded processes ; they have completely 

 coalesced behind, but are merely in apposition be- 

 tween the nasal sacs. The basi-trabecular (Fig. 2, B Tr) 

 is small, and the first pair of labials (1'), which together 

 with it form the " cutwater," are flat, and widely separated ; 

 the snout is consequently much blunter than in the adult. 

 The hypo-trabeculars (cornua trabecule of Rathke) occur 

 as two inturned S-shaped filaments of cartilage on either 

 side of the basi-trabecular : no trace of them is to be 

 found in the adult. 



III. — Skull of the Ray or Thornback (Raia clavata). — 

 On the whole the skull of the ray resembles very closely 

 that of the shark ; in some respects, however, it ap- 

 proaches more nearly to the higher fishes, and in others, 

 again, retains a lower or more embryonic character. 



One of the chief points of difference between this type 

 and the preceding is the much gre;iter elongation of the 

 skull, chiefly owing to the immense development of the 

 basi-trabecular (Fig. 5, BTr), which is produced to form 

 the long, stout rostrum, the apex of which is strengthened 

 by the first pair of labial cartilages (1'). The region 

 between the orbits is much pinched in, while the nasal 

 and auditory regions are extremely broad, the nose cap- 

 sules, especially, being as far apart as in the embryo 

 shark. On the upper surface, the prominences (epiotic, 

 pterotic, sphenotic) already described in the shark, are 

 seen ; but instead of one, there are two fontanelles, an 

 oval one between the nasal sacs, and a second of an 

 oblong shape, in the more normal position, between the 

 orbits. On the under surface of the nasal capsules are 

 seen the tecond, third, and fourth labials, forming a val- 

 vular apparatus for the nostrils ; the fifth labial and the 

 cxtra-branchials are absent. 



The upper and lower jaws or dentigerous arches closely 

 resemble those of the shark ; the opening of the mouth 

 is, however more completely on the under surface of the 

 head, as in the embryo Squaloid. In the front wall of 

 the spiracle a semi-lunar cartilage (M Pt) is found, con- 

 nected by ligament with the auditory capsule above, and 

 with the angle of the lower jaw below, and having the 

 same relations to the fifth and seventh nerves as the mela- 

 pterygoid ligament of the shark (Fig. 2, M Pt), or 

 the bone of the same name in the osseous fish ; this, 

 therefore, is the true apex of the mandibular or first post- 

 oral arch. 



There is no mistaking the hyo-mandibular (H M) a carti- 

 lage having precisely the same connection and relation to 

 the hinder division of the poriio dura as the part similarly 

 named in the shark, but much more slender, pointed below, 

 and inclined forwards. The remainder of the hyoid arch, 

 however, has taken on an entirely new character, and shows 

 a marked advance towards the Teleostian type, being at- 



tached, not to the lower part of the hyo-mandibular, but to 

 its upper posterior angle, by means of a band of liga- 

 mentous fibre, answering to the small styliform bone 

 (stylo-hyal of Cuvier) which in the osseous fish connects 

 the free portion of the hyoid with the suspensory appa- 

 ratus. The gill-bearing part of the hyoid is slenderer 

 than in the shark, and more highly segmented, being 

 divisible into epi- cerato-, and hypo-hyals (E Hy, C Hy, 

 H Hy) ; the basi-hyal or keystone-piece is absent. 



The branchial arches differ from those of the shark 

 chiefly in the great development of the inferior segment 

 or hypo-branchial. The first of these (H Br. i) is much 

 extended, and, uniting with its fellow of the opposite 

 side, forms a transverse bar behind Meckel's cartilage. 

 The second, third, and fourth hypo-branchials are broad 

 adze-shaped plates, while the fifth is coalesced with its 

 fellow in its hinder half, and extended forwards, so as 

 nearly to meet the corresponding piece of the first 

 arch. 



The youngest ray described was an embryo of R. 

 Diaciilaia, i \ inch long, taken from the purse at about the 

 seventh week from oviposition. The body proper is not 

 larger than that of the first stage of the dog-fish, the 

 greater length being due to the immense development of 

 the tail. The pectoral fins, which by their expansion and 

 union in front with the head, give to the adult ray its 

 peculiar depressed form, are at this age small semi- 

 elliptical lobes, one on each side of the umbilicus or point 

 of attachment of the large yolk-sac. Six or seven long 

 branchial filaments, expanded or spatulate at the end, are 

 attached to the hyoid and branchial arches, but none are 

 apparent externally on the mandibular. 



The facial arches are visible in a side view with perfect 

 distinctness, and have already advanced considerably in 

 segmentation, the apex of the mandibular being on the 

 point of separation so as to form the spiracular cartilage, 

 and the proximal end of the hyoid being cleft vertically, 

 thus separating the hyo-mandibular from the epi- 

 hyal. 



Three months after oviposition, although the yolk- 

 sac is still as large as a sinall walnut, the embryo has 

 completely taken on the adult form, the pectoral fins 

 having enlarged greatly, and brought the gill-slits to the 

 ventral surface ; from these the external branchia; still 

 project, being now in the form of long threads, almost 

 like the hyphre of a fungus ; the first cleft behind the 

 mouth (tympano-eustachian) remaining on the upper sur- 

 face has taken on the form of the spiracular opening. 



In the skull very few embryonic characteristics are left, 

 the chief being that the brain-case is rounder, the rostrum 

 shorter, and the two first labials separated from it by a 

 slight interval, instead of being in perfect apposition. 



METEOROLOGY OF THE WEST INDIES 



"T^HE hurricane season, here reckoned from July 25 to 

 -*■ October 25, went by without damage so far as 

 the Windward and Virgin Islands are concerned, though 

 not without disastrous examples of the phenomenon from 

 which it derives its name elsewhere. Two cyclones of 

 the ordinary kind have in fact visited these seas during 

 the above period ; and although neither of them included 

 the island of St. Thomas in its range, yet they passed 

 sufficiently near to make us aware of their exist- 

 ence, and to create considerable alarm among the 

 inhabitants. 



The first of these appears to have originated about Idt. 

 10" N. long. 55° W., on ornear August 10. Taking a north- 

 westerly direction it passed parallel with, but at a con- 

 siderable distance from the Wmdward islands, where from 

 August II to 13 the weather showed signs of great distur- 

 bance with violent squalls, that shifted to every part of 

 the compass ; while at Martinique in particular, where 



