144 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



ing the development of the ova which he studied a little farther along, 

 he would have learned, as he indeed surmises, tiiat the wreath of cells 

 becomes the thickened rim of the blastoderm, and that the portion of 

 the intermediary layer beneath the disk becomes the hypoblast. I see 

 no reason, however, for adopting the term blastodisc for the germinal 

 disk of the tish egg, for the whole of the latter, as well as the interme- 

 diary layer, are both unquestionably derived from the i^rimitive peri- 

 pheral germinal layer, the existence of which has been fully illustrated 

 and described in the lierring ovum by Kupfter,* though Costet describes 

 the formation of the germ in language which shows that he had un- 

 doubtedly seen and watched the T)rocess, which differs in different 

 species, as we shall learn when we come to discuss them. I reproduce 

 Coste's words belo w.| Knpffer describes the process minutely in the 

 herring, but states that the germ is never formed independently of the 

 action of the spermatozoan in that species, which is practically the fact 

 in the case of the shad and cod, but is not the case in ParepliipiniSy 

 CMrostoma, and Ceratacanthus, where a germinal disk is formed inde- 

 pendently of imi^regnation, but not until some time after the egg is laid. 

 Even in the three last-named species the process of the development of 

 the disk is the same, viz, the peripheral layer of germinal j^rotoplasm 

 aggregates at one pole of the vitellus. In some species, as in the her- 

 ring, shad, crab-eater, and stickleback, strands of protoplasm i)ass 

 inwards from the germinal layer among the yelk spheres or corpuscles 

 of the vitellus, so as to involve the latter in a sort of mesh work, which, 

 after the disk is formed, trend toward the center of the latter, forming 

 a i^rotoplasmic mass below the disk, and continuous with it, which prob- 

 ably fills a si^ace in the yelk below the disk, and which Kupffer calls 

 the "latebra" and Yan Beneden the ^'lentille." Upon close examina- 

 tion, however, these structures seem to me to be nothing but a portion 

 of the germinal disk, in consequence of their connection with the inter- 

 mediary layer lying between the latter and the vitelline globe or yelk. 

 The failure of more observers to witness the mode of development of 

 the germinal disk, and the fact that some have actually figured the seg- 

 mentation cavity without knowing what it was, is only explicable from 



* Die Entwickelimg desHerings im Ei, in Jakresbericht der Commissiou zur wissen- 

 schaftlichen Untersnchiiug der dentsclien Meere Id Kiel. 4to, Berlin, 1878, p. 181. 



tOrigine de la cicatricule ou du germe des poissons osseux. Comptes rendus, tome 

 30, 18r>0, p. 692. 



t"Ses ^16meuts g6n6rateur8 resteut ^pars, diss^min^s dans tons les points de ce 

 vitellns, jnsqu'an moment oii Taction du male les determine a se priScipiter vers una 

 region de la surface oil on les voit tons se r^unir jionr constituer le disque grauuleux 

 que la segmentation organise plus tard." 



"Quand cette curieuse e;/)i^/-aiio« des granules mol^cnlaires que doivent former la 

 cicatricule s'est op6r6e, I'ceuf des poissons osseux ressemble alors, mais alors seulement, 

 h celui des oiseaux." 



The writer, in explaining the formation of the- germinal disk, is in the habit of 

 describing it as an aniwboid mijiration of the germinal matter toward one point on the 

 Titellus, which is essentially the meaning of this quotation; but the germinal matter 

 is not always mixed among the vitelline corpuscles, as Coste describes in Gasterosteus, 

 It is the case in Clupea and Alosa, but not in Gadus, CyMum, ov Belone. 



