OP ARTS AND SCIENCES. 65 



although contending that it forms no part of the real hypoblast. In 

 former papers on the Spanish Mackerel and Silver Gar, he held to the 

 opinion maintained by KupfFer and others, namely, that the periblast 

 was truly hypoblustic : but finding no connection between it and the 

 cells which form the alimentary tract, he concludes that it is only "a 

 temporary and evanescent structure, which vanishes completely when 

 the contained yolk material has been absorbed" (No. 57, p. 185), 

 and that therefore it cannot properly be called " one of the primary 

 embryonic layers." 



In a recent paper (No. 21) Waldeyer has discussed at length the 

 relations of the " archiblast " and the " parablast," claiming, in oppo- 

 sition to His, that they are one in origin. With reference to the 

 origin of what we have called periblastic cells, he remarks (p. 31) : 

 '• So far as my observations go, in thin sections of hardened prepa- 

 rations, nuclei, apparently free, are seen to appear in the pellicle of 

 the teleostean ovum, as well as in the subgerminal yolk-layer, which 

 multiply by division." The appearance of distinct cell limits around 

 these nuclei at a comparatively late date, is defined as a "■ secondary 

 cleavage." Speaking of the meroblastic ovum in a general way, he 

 says : " The cleavage of the eggs of all those animals in which blood 

 and connective tissue occur, is not uniform from beginning to end ; 

 but a primary and a secondary cleavage must be distinguished. The 

 first divides the egg, so far as it is capable of cleavage, into a number 

 of cells which are ripe for the formation of tissues. These form, then, 

 the primary germ-layers. A remainder of unripe cleavage-cells (in 

 holoblastic eggs), or of protoplasm which has not yet been trans- 

 formed into cells (in meroblastic eggs), is left over." (pp. 47, 48.) 

 A secondary cleavage later makes cells out of this remainder. " When 

 the cleavage of the germinal disc is concluded, the pellicle [Riuden- 

 protoplasma] and the subgerminal processes [Keimfortsiitze] begin 

 to break up into cells. These cells are smaller than those of the 

 germinal disc, and naturally lie at first beneath the disc, especially 

 beneath its margin, where they are imbedded in the white yolk, and 



also in the pellicle [Dotterrinde] This process is very easily 



seen in the bony fishes, where it has often been described." (p. 15.) 



With reference to the fate of the archiblast and the parablast, 

 AValdeyer agrees, in the main, with Ilis. He derives the blood and 

 connective tissue from the '' Rindenprotoplasma und aus den in den 

 Dotter eingesenkten Protoplasmafortsiltzen, den ' Keimfortsiitzen,' wie 

 ich sie genannt habe." 



Kupffer, in his work on the Ostseeharing, also draws a sharp line 



VOL. XX. (X. S. XT I.) 5 



