EMBRYOLOGY OF CLEPSINE. 257 



The occurrence of polar globules is still a matter of doubt in 

 Birds, Reptiles, Aniphibiaus, most Fishes, Tunicates, Arthropods, 

 and Rotifers. The elimination of the entire germinal vesical, as 

 represented by Balfour and Oellacher, for Birds and Fishes, can 

 hardly be compared to the production of polar globules by 

 amphiastral division. The same may be said of the thin veil of 

 substance found on the animal pole of the amphibian egg, after 

 the disappearance of the germinal vesicle. 



The '■' pole- cells" which appear on the aboral end of the egg 

 of insects, notwithstanding that their genetic relation with the ger- 

 minal vesicle, is now an estabHshed fact (li^), cannot, in con- 

 sequence of their forming the basis of the sexual organs (Miastor, 

 Chironomus, Ii4)> ^^ compared with the directive corpuscles. 



The so-called ''testa-cells" (** Testa-tropfen,"^ Semper) of As- 

 cidiam arise, according to KupfFer, Metschnikoff, and Semper, 

 from the yolk — according to StepanofF and Kowalevsky, from the 

 follicle-cells. In neither case case can they be compared, as Sem- 

 per (tit^xt) ^^s done, with the polar globules, since they arise not 

 only before fecundation {-yi^), but also before the transformation 

 of the germinal vesicle (-f^, ■g^o'V) . Semper is equally unfortunate 

 in this comparison in other respects. He declares that the " tes- 

 tadrops " arise simultaneously with the cleavage ; but in no case 

 is this true of polar globules. He states furthermore that neither 

 the *' testa-drops " nor polar globules have nuclei, and that they 

 both move freely around the egg, all of which we now know is 

 entirely incorrect so far as it concerns the polar globules. 



Various opinions have prevailed in regard to the morphological 

 value of these corpuscles. Older authors (Dumortier, Pouchet, 

 van Beneden, sen., Reichert, KoUiker, Vogt, Bischoff, Loven, 

 &c.) from the time of their discovery by Cams in 1824 up to 

 1848, supposed that they represented either the germinal spot 

 or the germinal vesicle. Rathke (-ri^Vg^, 1848), whose views 

 received the assent of most naturalists up to a very recent date, 

 maintained tliat they were unimportant drom of liquor vltelli, 

 expelled by contractions of the yolk during cleavage, precisely 

 such as are seem to come out of the egg if it be artiticially 

 pressed. According to Robin (o^/s^tt) they originate pecisely as 

 the first four ectoderm-cells (Hirudinea) and the blastoderm-cells 

 (lii!se(ts1, all of which he represents as arising by a process of 

 " budding " from the protoplasm of the egg, without the aid of 

 nuclear elements. " En resume, c'est par le mode d'individuaii- 

 sation des elements anatomiques, appele gemmation et s' operant 

 a Taide et aux depens de la substance hyaline du vitellus, que 

 naissent les globules polaires " (-^-f). Fol (41) and Biitschli 

 (27) were the first to show in a decisive manner a geuetic rela- 

 tion betvi-eeu the polar globules and the germinal vesicle ; and 



