528 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. [74] 



with which the hind-gut and neurula are conterminous posteriorly, must 

 in its mesial or axial portion represent the nourenteric canal, though an 

 actual tubular intercommunication of the gut and neurula are never 

 developed as in the embryos of Ampliioxus. While, therefore, it is not 

 yet possible to assert that there is a true gastrula mouth (prostoma) 

 developetl, in the embryos of Teleostei, we are in a position to say that, 

 inasmuch as the rim of the blastoderm is used up in the formation of 

 the caudal plate, which is taken up into the posterior portion of the 

 body, the true blastopore probably coincides with the last jiortion of 

 the solid neurula, to be formed at the anterior border of the yelk bias, 

 topore, and cannot be identified with the latter itself. The latter is not, 

 therefore, homologous with the blastopore of the frog's ovum. I cannot 

 accept the views of Zeigler in regard to the homologies which he has 

 sought to establish betv/een the whole of the Teleosteau and amphibian 

 ovum, for reasons relating partly to the history of the blastopore and 

 partly on account of considerations which arise from a stud}" of the fate 

 of the yelk. 



In embryos of the cod on the sixteenth day of development. Fig. 32, 

 the intestine has made a very notable advance in differentiation as com- 

 pared with the stage shown in Fig. 31. In the anterior portion it has 

 barely acquired a lumen, and is still much depressed; but farther back 

 from a little in front of the breast fin to the vent v it has gained in ver- 

 tical thickness very notably, become more cylindrical, and has acquired 

 a central cavity. Its anal end apparently terminates upon the yelk. 

 Just opposite the pectoral fin-fold ff the ventral wall of the intestine is 

 becoming quite thick in the vicinity of Iv. This thickening represents 

 the rudiment of the liver, which appears in the cod, as in other fishes, 

 to be at first a solid outgrowth fi-om the intestine. The condition of 

 the intestine on the sixteenth day, as in Fig. 32, is gradually followed 

 by a more advanced state, such as that shown in Fig. 34, taken from 

 an embryo on the nineteenth day of incubation. It is shortly after or 

 at about this stage that the anal end of the intestine is carried outwards 

 to end in the ventral fin-fold, some distance above its margin, as shown 

 in the just-hatched embryo represented in Fig. 40. The rudiment of 

 the liver in Fig. 34 has beeu more fully developed, and now projects as 

 a lateral, ventral, and dorsal thickening of the intestinal wall at Iv. It 

 has not yet apparently acquired a lobulated structure, such as after- 

 wards becomes apparent in more advanced stages. As the develop- 

 ment of the liver proceeds it becomes gradually more conspicuous as a 

 lobulated organ on the left side of the intestine, but is reflected around 

 the latter above and below, as shown in Fig. 40. From the time of 

 hatching onwards the intestine gradually acquires a spacious lumen, 

 but no greeni.sh biliary secretion was noticed in it, such as is commonly 

 observed at this stage in embryos of Cottus, ISalmo, etc., of the same age. 

 It is singular that the secretion of bile in fish embryos should precede 



