646 BASHFOKD DEAN, 



in PL 9, Fig. 5. The continued elongation of the tail in this stage, 

 taking place within the egg membranes, is accompanied with the 

 torsion of the hinder trunk; this, turning on its side, now grows flat- 

 wise, opposing (usually) its left side to the yolk-sac; and in its later 

 growth it assumes a somewhat S-shaped position. Its terminal is 

 still rounded. The entire trunk is whitish, pigmentless, semitrans- 

 parent; toward its hinder part the somites become more and more 

 difficult to distinguish. 



Larva at hatching (PI. 9, Fig. 6 and, in dorsal view, Fig. 7). 

 The embryo exhibits movements for nearly a day before hatch- 

 ing; these become especially noteworthy a few hours before the 

 escape from the egg membranes, the tail writhing sometimes slowly, 

 sometimes quickly and spasmodically, from side to side. The move- 

 ments must undoubtedly be looked upon as the efficient cause of the 

 escape of the embryo from the egg, although during the later stages 

 a decided thinning and drying up of the membranes is to be noted. 

 Upon detaching itself from its membranes the larva lies quietly on 

 its side for some hours, rarely moving. Its head and trunk are 

 whitish, still without pigment; the great rounded yolk sac is pale 

 slate-coloured, in its region below the head a faint tinge of colour 

 indicates the position of the heart. As seen in the figure, PI. 9, 

 Fig. 6, the body length is somewhat downbent, the tail drooping 

 ventrally to the level of the base of the yolk sac. The conditions of 

 the Organs at this stage can readily be made out in the living larva 

 an account of its transparency ; the relatively large size of the optic 

 lobes, the breadth and openness of the fourth ventricle are to be 

 noted; the heart is as yet unbent, a short thick tube from whose 

 hinder end diverge the omphalo-mesenteric veins ; the mouth pit is 

 just on the point of establishing its opening into the fore-gut, the 

 proctodaeum, a sharp nick on the margin of the fin membrane, has not 

 as yet its connection with the bind gut; the gill region is consider- 

 ably flattened, dorso- ventrally, against the outswelling yolk; the fifth 

 gill slit is determinable. In the eyes there are as yet but traces of 

 pigment and the lens has not been completely formed. The body 

 Segments are to be traced into the hinder trunk but are not as yet 

 ditferentiated near the bulbous tip of the tail; there is no post-anal 

 gut; the unpaired fins are noticeable, but still inconspicuous ; there is 

 as yet little trace of the pectoral fins ; the liver is now coraing to 

 be formed, distinguishable as a whitened tract on the yolk region at 



