No. 3.] STUDIES ON CEPHALOPODS. 26 1 



on the early development phenomena of the various forms of 

 Daphnidse, I constructed the following table, which shows at a 

 glance the intimate connection existing between the so-called 

 " types " of cleavage and the relative amount of deutoplasm 

 contained in the protoplasm of the ^gg, and this conclusively, 

 because the difference in cleavage is seen in the ova of one and 

 the same species of animal. 



Broods of Eggs. Types of Quajttily of 



Cleavage, food-yolk. 



Polyphemus oculus { '^^^^^^ holoblastic scanty. 



•- Winter meroblastic plenty. 



Bythotrephes longimanus. { ^^"""^^"^ holoblastic scanty. 



•- Winter meroblastic plenty. 



Moina rectirostris { S^"^'"" holoblastic scanty. 



^ Winter meroblastic plenty. 



Leptodora hyalina | ^"."^"^^'^ meroblastic plenty. 



<- Winter meroblastic plenty. 



/ Summer meroblastic plenty. 



t- Winter meroblastic plenty. 



Daphina loitgispina 



In Leptodora and DapJinia, both the winter and summer eggs 

 contain plenty of food-yolk, so that the cleavage is not com- 

 plete ; while in PolypJienuis, BytJiotrcpJies, and Moina, the dif- 

 ference between the cleavage of winter and summer eggs are 

 so sharply marked that the two broods of eggs may be taken 

 for two entirely different organisms, if the affinity of the 

 "types" of cleavage of the ova were in any way indicative of 

 the systematic affinity of the adult organisms. The same may 

 be said in regard to the cleavages in different species of Peripatus, 

 as the studies of Sedgwick and others have shown. The same 

 is true in the case of Renilla, as was shown by Wilson. In 

 short, if we classify animals by the "types" of cleavage, or 

 differences of cleavage, rather than with reference to the poten- 

 tial qualities of the nuclear substance, we fall into an error of 

 placing nearly related species of organisms in different cate- 

 gories ; nay, we even fall into the absurdity of separating the 

 individuals of one and the same species into different groups. 



Sachs ^ gives an instance illustrating the same fact in plants ; 

 viz. six different forms of cleavage taking place in the pollen 

 mother-cells from one and the same orchid, the difference in 

 cleavage being produced by the slight individual variation in 



1 loc. cit. 



