532 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [78] 



aud thickest. Ilcre, probably, we have the first evidence of the devel- 

 meut of true gastric follicles. Of the developraeut of the i)yloiic ap- 

 pendages I can say nothing more than that they, like the liver, are 

 undoubtedly diverticula of the intestine, but which evidently develop 

 much later than that organ, for in no form studied by me had they 

 made their appearance up to the time, and even as late as two weeks 

 •after, the yelk was absorbed. 



The vent of young fishes at first ends blindly. At the very moment 

 the tail begins to bud out as a little rounded knob-like prominence the 

 anal end of the gut breaks its continuity with the caudal uuiss of cells, 

 and its blind extremity is directed straight backwards. Meanwhile the 

 rest of the tail continues to grow backwards in length, leaving the anal 

 end of the gut in the angle formed between the lower border of the tail 

 and the yelk-sack, as shown in Fig. 40. In transverse sections of the 

 tail of embryos a little younger than that shown in Fig. 32, a ventral 

 strand of cells may be seen which appear to have been continued back- 

 wards from the anal end of the gut into the caudal mass of cells, but it 

 is difficult to assure one's self that they inclose a canal which would an- 

 swer to a post-anal section of the intestine, the homologue of the neu- 

 renteric canal. At this stage the anal end of the gut is sometimes 

 club-shaped, and may end apparently on the yelk, as in the young cod, 

 or may soon be slightly prolonged backwards and ventral wards between 

 the thin dermal and splanchnopleural layers to end in an emarginatiou 

 at the edge of the ventral median fin-fold. This mode of termination 

 is the usual one, and, so far as I am aware, the embryo cod is the only 

 exception to it. Here, instead of ending at the margin of the fin-fold, 

 the vent does not grow out so far, but ends within the margin of the 

 fin-fold aud some way from it, as may be seen in Figs. 40, 45, and 40. 

 Moreover, with the outgrowth of the tail there is no marked accom- 

 panying prolongation of the hind section of the gut, such as we may 

 note in young of Salmo, Coregomis, Alosa^ Fomolobus, and Clupea. In 

 these forms as the growth of the tail proceeds the anal end of the intes- 

 tine, on the contrary, makes an accompanying growth in length back- 

 wards, by which the vent is pushed farther and farther back Irom the 

 posterior end of the yelk-sack. Another type of development of the 

 hind-gut of the embryos of osseous fi«hes is met with in Gyhhim and 

 Farephippus, where the hind-gut grows out to the margin of the ventral 

 finfold, but is not prolonged backward behind the yelk-sack, in con- 

 sequence of the subsequent growth in length of the tail. With the col- 

 lapse of the yelk-sack, however, in these two genera, the pre-anal fin-fold 

 lengthens; thiv. lengthening of the latter fold is, however, wholly ascrib- 

 able, to the collai)se of the yelk-sack, and not to any backward growth 

 in length of the tail as a whole. 



Of the develoi)ment of the sjileen and ])ancreatic tissues I can add 

 nothing to what is already known, which is very little, except that in 

 Oambusia I have met what may i)ossibly be a splenic rudiment behind 



