1884.] 143 [Hyatt. 



form or zoon, when compared with the full grown Amoeba. If 

 descent from Amoebae, through Flagellata and Ciliata is assumed, 

 then the task of proving young cells to be immature forms 

 becomes easier. In this case they are obviously forms, which, like 

 the ova of many Metazoa, have retained their ancient, amoeboidal 

 characteristics while losing their later acquired flagellate and cili- 

 ate similarities. We cannot use the words embryo and larva, 

 which belong to the ovum after impregnation, and we, therefore, 

 propose to designate the cell an autotemnon, 1 in contrast with the 

 embryo which is more specialized. The least specialized tis- 

 sue cells of the mesenchyme differ least from the individualized 

 agamic zoons of the Protozoa ; while the spermatocysts, as more 

 highly specialized, encysted male zoons, retain the cycle of 

 agamic transformations derived from their male Protozoonal pro- 

 totypes, and are intermediate to the encysted female zoon or 

 ovum. The spermatocyst, in other words, is not dependent upon 

 impregnation for its development and has necessarily retained 

 more of the characteristic, successive transformations of the prim- 

 itive agamic form than the ovum. This last has become depen- 

 dent upon impregnation. The tendency to earlier and earlier 

 impregnation in successive generations, and the correllative con- 

 centration of useless autotemnic stages has finally established the 

 ovum as a more highly specialized form of cell. 



The conditions under which fission occurs in the cyst, and in 

 the ovum and spermatocyst are similar as long as the zoons or 

 cells are all similarly confined, but when they burst the envelope 

 and become free, the surrounding conditions differ and they cor- 

 respondingly diverge. 



The early encystment of the ovum, the non-production of the 

 colonial form by incomplete fission, the dependence of the femi- 

 nonucleus upon impregnation, and the great rapidity and exten- 

 sive character of the changes by which the diploblastic paren- 

 chymula and triploblastic gastrula are built up, all show the 

 excessive concentration of development which has taken place, 

 when any blastula is compared with the corresponding forms 

 among the Volvocinae. There is also a distinction between the 

 mode of development of the Volvocinae, and the lower Proto- 



1 From av'rds, self, and Te'jjivw, to divide. 



