EMBRYOLOGY OF CLEPSINE. 309 



of the primary entoderm. I have before called attention to the 

 general occurrence of free nuclei^ especially in the case of dis- 

 coidal development. In the egg of the fish and the bird the 

 ectoderm develops from the upper pole. The lower pole is 

 primary entoderm^ so enormously distended with nutritive yolk 

 (deutoplasm), that no regular cleavage takes place. But here, 

 as in Clepsine, free nuclei form in the periphery of the yolk, and 

 later become the centres of cells. That these cells form the 

 entoderm in the fish and the bird, as in Clepsine, is highly pro- 

 bable as appears from what was said under the head of free 

 nuclei and entoderm. I may here call attention to a significant 

 remark by Rauber (i4t)- Speaking of free nuclei which are 

 formed even oiitside the embryonic rim in the bird's e^^, he 

 says : It looks as if we had to do with a superficial cleavage, the 

 products of which are added to those of the blastodisc. . . . 

 Future investigation will have to teach us whether the entoderm 

 is jnirtli/ formed in this xoay^ It was with no small degree of 

 pleasure that I read the following remarks by van Beneden.i 

 Comparing the development of the Dicyemida with the early 

 phases of evolution m the fish, van Beneden says : " Dans le 

 manteau protoplasmique du globe vitellin (couche intermediaire 

 de van Bambeke) se dcveloppe a la fois, par voie endogene, toute 

 une generation de noyaux. Autour de chacuu de ces noyaux se 

 delimite un corps cellulaire ; il en fi'sulte la formation d'line 

 caliche distincte de cellules; c'esi Vendoderine. C'est de cette 

 maniere que j'interprete les recherches de Kupfi'er, de van Bam- 

 beke, de Balfour, et de Klein " (-rH-^)- 



The same view is more fully given in an article published m 

 this Journal January, 1878. (161). 



Bibliography. 



1. A. Agassiz. — Embryology of the Starfish, from vol. v of L. Agassiz's 

 ' Coutrib. to Nat. Hist, of U. S. A.' Cambridge, Mass., Dec., 1SG4. 



2. Id. — Embryology of the Cteuophora, 'Mem. of the Amer. Acad, of 

 Arts and Sci.,' vol. x, p. 357= 1873. 



3. Auerbach. — Organologiscbe Studieu. Breslau, 1874;. 



4. Baer. — Entwicklungsgeschichte der Thiere. Kouigsberg, 182S. 



.5. Id. — Die Metamorphose des Eies der Batrachier, ' Miil. Arch.,' p. 

 481. 1834. 



6. Id. — Neue Untersuchuugen ueber die Entwicklung der Thiere, from 

 ' Neue Notizen aus dem Gebiete der Natur uud Heilkunde,' vol. xxxix, p. 

 32. 1846. 



7. Id. — Studien aus dem Gebiete der Naturwissenschaften, vol. ii. 1876. 



8. Bambelce. — Embryogenie. Premiers effets de la fecundation sur les 

 oeufs de poissons, 'Compt. rend, des seances de 1' Acad, des Sci.,' tome 

 Ixxiv, No. 16, p. 4. 1872. 



' Myopinion was formed entirely independently of these remarks. 



