June II, 1874] 



NA TURE 



107 



by the agency of a leaven or ferment which is contained 

 in the stomach-juice, and can be, like the ferment of saliva, 

 easily separated and prepared. As so separated, it is 

 called pepsin (the medicine called by that name is 

 supposed to contain some ot it, and indeed often does). 

 Consequently, having the ferment, we can easily imitate 

 digestion out of the body. For this experiment there are 

 three things necessary— first, that our liquid should con- 

 tain pepsin ; secondly, that it should be slightly acid ; and 

 thirdly, that it should be kept at the temperature of incu- 

 bation, /.(•. about 97° F. We select for the experiment a 

 substance which, ahhough nutritious and containing nitro- 

 gen, is not easily digested — such, for example, as boiled 

 white of egg. In water containing a small percentage of 

 hydrochloric acid and a trace of pepsin, it is gradually 

 dissolved ; but chemical examination of the liquid shows us 

 that it has not been destroyed, but merely transformed 

 into a new substance, called peptone, which is afterwards 

 absorbed, i.e. taken into the circulating blood. 



Between this process and the digestion of the Dionsa 

 leaf, the resemblance, as Mr. Darwin has found by a most 

 elaborate comparative investigation, is complete. It 

 digests exactly the same substances in exactly the same 

 way, ix. it digests the albuminous constituents of the 

 bodies of animals just as we digest them. In both in- 

 stances it is essential that the body to be digested should 

 be steeped in a liquid, which in Diona^a is secreted by 

 the red glands on the upper surface of the leaf; in the 

 other case, by the glands of the mucous membrane. In 

 both the act of secretion is excited by the presence of the 

 substance to be digested. In the leaf, just as in the 

 stomach, the secretion is not poured out unless there is 

 something nutritious contained in it for it to act upon, 

 and finally in both cases the secretion is acid. As regards 

 the stomach, we know what the acid is : it is hydro- 

 chloric acid. As regards the leaf, we do not know precisely 

 as yet, but I\Ir. Darwin has been able to arrive at very 

 probable conclusions, the setting forth of w'hich we look 

 forward to in his expected work on the Droseracex. 

 (To be coatiiiuecf.) 



REPORT OF PROF. PARKER'S HUNTERIAN 

 LECTURES "ON THE STRUCTURE AND 

 DEVELOPMENT OF THE VERTEBRATE 

 SKULL"* 



IV. 



IN the Teleostei the jaws attain their maximum amount 

 of mobility, and the articulation of the lower jaw is, 

 consequently, brought to the farthest possible distance from 

 the skull, by the disjointing of the mandibular arch from 

 its original attachment. This arch consists of two carti- 

 laginous bars (see Fig. 11, Pl.Pt and Mck) correspond- 

 ing to the upper and lower jaws of the shark or ray, but 

 containirg certain important ossifications. The apex of 

 the arch, corresponding to the spiracular cartilage of the 

 ray, is formed by the meta-pterygoid (Fig. 7, M.Pt), 

 below which, and separated from it by a broad synchon- 

 drosis, is the quadrate (Ou) bearing a rounded articular 

 surface for the mandible. In the pterygo-palatine carti- 

 lage are three ossifications — the palatine (PI), pterygoid 

 (hidden in the figure by the maxilla and jugal),and mcso- 

 pterygoid (Ms.Pt). The proximal portion of the origi- 

 nally cartilaginous lower jaw is ossified by the articular 

 (Art), while its distal portion remains as the comparatively 

 slender Meckel's cartilage, running on the inner side of 

 the dentary, almost to the symphysis. 



As in the Elamobranchs, the proximal part of the hyoid 

 arch forms the suspensory apparatus for the jaws, but 

 unlike the corresponding cartilage in those fi;h, contains 

 two ossifications, the large and massive hyo-:r.andibular 

 (H.M), articulating with a cartilaginous surface afforded to 

 it by the sphenolic and pterotic (see Fig. 9), and the sym- 



" Continued from p rn. 



plectic (Sy) below, which, fitting into a groove in the 

 quadrate, firmly binds together the hyoid and man- 

 dibular arches. The free portion of the hyoid arti- 

 culates with the cartilaginous space between the 

 hyo-mandibular and symplectic, through the intermedi- 

 ation of a small bone (shown in Fig. 7 by dotted lines, 

 being hidden by the pre-opercular), called by Cuvier the' 

 stylo-hyal, but better named inter-hyal, as it is not the 

 homologue of the mammalian styloid process. The hyoid 

 cornu is segmented as in the ray, except for the fact 

 that there is a median basal piece, usually called, from 

 the circumstance of its giving support to the tongue, 

 glosso-hyal (G.Hy). All these segments are ossified and 

 separated from one another by tracts of cartilage. 



The branchial arches are much smaller in proportion 

 to the mandibular and hyoid than in the shark and ray ; 

 they also lie almost entirely within the latter, instead of 

 in a regular series behind it. Each of the first four bars 

 is divided into pharyngo-, epi-, cerato-, hypo-, and basi- 

 branchial ; and each segment, with the exception of the 

 last pharyngo-branchial, is ossified. The fifth arch (in- 

 ferior pharyngeal bone) is much smaller than its predeces- 

 sors, and consists simply of a tooth-bearing cerato-bran- 

 chial. The pharyngo-branchials (superior pharyngeal 

 bones) are not dentigerous. 



The development of the sdtnon was described at far 

 greater length than that of the shark or ray, the meta- 

 morphoses gone through being much more complex, and 

 exhibiting in a most instructive manner the endless modi- 

 fications which the facial arches may undergo in their 

 modes of segmentation and coalescence. 



Besides the adult, seven arbitrary stages of the skull 

 were described ; in the first three of which the embryo 

 was still unhatched, and lying as a flat tape-like band 

 about :,; of an inch long coiled round the yelksac ; in the 

 fourth the head was just emerging from the chorion ; the 

 fifth consisted of salmon fry at the second week after 

 hatching ; those of the sixth stage were at the sixth week; 

 and those of the seventh young salmon of the Irrst summer, 

 varying in length from I A to 2^ inches, and having in all 

 essential respects the cranial ch:iract;rs of the cdult. The 

 earliest stages are remarkable for their want of symmetry, 

 the head being so twisted that only one eye is visible in 

 an upper view. 



The head of an embryo at the first of these stages is 

 shown in Fig. 10; it resembles very closely the earliest con. 

 ditions in the shark and ray (Figs. 3 and 6, vol. ix. p. 467), 

 having, like them, prominent sense-capsules, a widely- 

 open mouth, and simple, unsegmented facial arches, 

 which latier, however, present very important differences 

 to the homologous structures in the lower types. The 

 trabecular (Tr) are seen in the roof of the mouth, where 

 they lie, enclosing the pituitaiy body (Pty) like a pair of 

 forceps, in the same plane as the investing mass and 

 notochord, and not at right angles to them like the post- 

 oral arches. Curving under the eye is a bar of somewhat 

 thickened indifferent tissue (Pl.Pt) representing the 

 pterygo-palatine arcade, but, even in this extremely early 

 stage, so entirely distinct from the mandibular arch 

 proper (i\In) as to have the appearance of a true, separate 

 face-bar. It long remains, however, in a rudimentary 

 state as regards histological development, not beir-g con- 

 verted into true hyaline cartilage until the fourth stage, 

 when it unites with the main part of the mandibular arch. 



In the second stage, a most noticeable change has 

 taken place with regard to the hyoid. A lozenge-shaped 

 basal piece, the glosso-hyal, has appeared between the 

 bars of opposite sides, and the whole arch has split 

 lengthwise Irom top to bottom, becoming divided into an 

 anterior and posterior division, the former of uhicli be- 

 comes the fixed hyo-mandibular and symplectic, ths Litter 

 the free epi- and cerato- hy.ils. 



In the third stage, this process has gone fa th.r : the 

 two divisions of the hyoid have become sepa'aied from 



