19 



The opening of the nose on the top of the head, lies in tlie frontal plane between the angle of the mouth and 

 the eye fissure; it has a tendency to become semilunar, witli the concavity to the back. The full front margin encroaches 

 so to speak, at its corners, on the somewhat full hind margin, which bears in the middle a slightly raised spot of colour. 



The previously very oblique eye fissure gradually assumes a horizontal position, i. e. parallel with the long axis 

 of the body. The eye region now begins to be less prominent. The ear aperture which is very indistinct and difficult to 

 tind, lies from 4 to 6 millim. behind, and a little below the eye cleft. 



The upper contour of the head above the nose describes a sharp, convex curve at the back of the head, before 

 it joins the almost straight line of the back. The occipital region is thus the most convex part. No neck segment is now 

 distinguishable. 



The greatest thickness of the trunk is immediately in front of the insertion of the umbilical cord and the dorsal 

 tin, whence it tapers backwards like a narrow cone slightly compressed at the sides. The contour of the back is somewhat 

 straighter in front of the dorsal tin (still with a slight concavity at the neck in the younger fætusj, and behind it, is convex 

 to the very end of the tail, concerning which further remarks will be found below. In the contour of the abdomen, there is 

 a slight concavity between the pectorals, which gradually decreases in the larger embryos, until, in the umbilical region, a 

 slight convexity is formed, while the lateral curve of the tail generally begins in the region behind the anus. 



The pectoral fins are situated somewhat behind the front fourth part of the body. As before stated, they amount 

 to fi'om '/4.J to \io,H of the length of the body. Their convex ventral margin has a slight depression in the region of the 

 carpus. The dorsal margin is sharp, and forms, in its larger distal portion, a concave half-moon (fig. 2), followed by a 

 triangular protuberance, which, in its turn, merges into a straight or concave, less sharp, proximal portion. As regards the 

 position of the pectorals, they lie more or less against the ventral surface, or project, so that their dorsal surface is parallel 

 with the side surface of the body. 



The triangular dorsal fin forms, in the smaller embryos (tig. 1), a semilunar protuberance, from 3 to 5 millim. 

 in height, with no sharp boundary-line defining its base from the surface of the back. In the larger fætus (fig. 2) where 

 the dorsal fin is from 8 to 10 millim. high, its base limit becomes more clearly defined; the highest point of the fin, which 

 was formerly rounded, is now more pointed, the gently ascending front margin is distinguished by its shape from the slightly 

 concave, and nmch more abruptly descending hind margin, the dorsal fin, as a whole, thus approximating more to the form 

 characteristic of the genus (fig. 2). The tVrtal character is, however, still prominent in its relative position, which is almost 

 opposite to the insertion of the umbilical cord, though in such a manner that the point of the dorsal fin lies rather behind 

 a transversal plane through the former. The posterior margin of the dorsal fin is continued as a low keel for a siiort distance 

 Ijackwards down the median line of the back. 



In the median line of the abdominal surface there is a raphe in the form of a fine, whitish Hue; in the smaller 

 embryos, around the insertion of the uinliiliral cord, there is often visible a field, pointed at Ijoth ends, and separated from 

 the side regions by a conspicuous groove, recalling the conditions in the earlier stages. 



The genitalia externa at this stage, are of considerable interest. Most of the fætuses were females, only a 

 small luimber being males, viz. 16 females and 8 males. 



The entrance to the female genital aperture is for the most part covered by the greatly developed clitoris, wjiich 

 forms a caudally-directed hook with a broad base. Around this and the sexual aperture, which is an open, oval cavity, the 

 skin is puffed up into incipient labia nmjora. Immediately to the side of the sexual fissure, and separated from it only by 

 a shallow furrow, the manimæ pudendales come into view like little prominences, one on either side, with a small iissure-like 

 depression on the top of each. Immediately behind the sexual aperture, the anus may be detected, looking like a small 

 liuncture-like opening. 



In the male fætuses the external genitalia are in the form of an anteriorly tapering elevation. The process-like 

 penis, from 3 to i millim. in length, points in a forward direction, and protrudes from a cylindrical skin sheath (preputiumi 

 which posteriorly merges gradually into the skin. In the median line there is a raphe up to the anus. In the full part 

 lying iK'hind the preputium, two small depressions may be detected, lying close to one another, indications of the rudimentary 

 mamnue masculinæ. 



The tail or "postanal" portion of the trunk is, at this stadium, compressed at the sides, and rather high, forming 

 on the dorsal and ventral surfaces a sharp ridge, from the distal part of wiiich project the triangular side-lobes, forming a 

 somewhat convex dorsal surface, and a slightly concave ventral surface. In tlie larger fætuses the hind margin has a sigmoid 

 curvature, with a cleft in the middle tiie side points still being rounded. Tiie tail, as already stated, inclines, in the larger 

 fd'tus (fig. 2) to one side, either the right or the left. This side inclination is more developed in later fVetal existence, 

 so that in the full-grown f(etus, the tail is always found pressed up against one side, thus occupying a smaller space in the uterus. 



The colouring of the skin. The distribution of colour over the skin of fætuses in this stadium is a subject 

 of extreme interest. The darkly coloured "neck-band" mentioned in the previous stadium, is, in fætuses of from 10 to 20 



