196 Mr. A. Hyatt on the 



get no further tlian the production of single ova and sperma- 

 tocysts *, or the earliest stages of segmentation, during the 

 same period. The adult condition of Eudorina or Volvox in 

 other words is a permanent morphological equivalent of the 

 blastula stage in the ovum of a Metazoon, and a spermato- 

 cyst holds a similar relation to the encysted reproductive stage 

 at the terminus of life in an Amoeba. It, however, occurs at 

 the beginning of life in this specialized male cell among 

 Metazoa. The spermatozoa also, which are produced by 

 fission of the nucleus, resemble the young of the Aracebinse 

 and many other Protozoa in form, but have, through earlier 

 inheritance of characteristics, acquired the functional power 

 of the adult male Protozoon, and are therefore, as compared 

 with Protozoa, to be estimated morphologically and function- 

 ally as microgonids with highly concentrated development. 

 In no other way can we account for the premature exhibition 

 of power shown by these forms in seeking out the Qgg and 

 forcing their way into the vitellus. Ultimate union with the 

 female nucleus of the ovum by passage through the vitellus 

 is quite distinct. It has appeared to us to be, like concres- 

 cence in low forms, an exhibition of mutual attraction which 

 indicates affinity, and, like all sexual processes, a vital attrac- 

 tion of greater intensity than mere fusion by growth, and in 

 no way attributable to accident. The habit may have sprung 

 from the habit of concrescence, just as we can only imagine 

 all sexual processes as springing originally from concrescence 

 through its transformation into a habit preparatory to repro- 

 duction by division, as among Myxomycetes. Cienkowski 

 considers concrescence to have originated from the habit of 

 feeding, and the results of concrescence, reproduction by 

 fission, as a function due to the same causes and having the 

 same results as assimilation (Archiv mikr. Anat. vol. ix.). 



There is a gradation in the stages of development of the 

 ectoderm, endoderm, and mesenchyme in the sponges which 

 shows they have retained the ancestral protozoonal character- 

 istics in some cells more than in others. Thus the ectoderm ic 

 cells in all the Porifera become permanently transformed into 

 flat epithelial cells, losing their feeding-organs, the collars, 

 and flagella ; whereas the cells of the endoderm in some forms, 

 such as the Ascones, probably never lose these organs at all, 

 and in others lose them only transiently at certain stages, or 



* For results of protection in producing concentration of development 

 s^e " Geuet^is of Planoihis at Steiulieini," Mem. Bost. Soc. Nat. Hist. 

 J. Anniv. 1830-1880; Fossil Ceph., Mus. Comp. Zool., Proc. Amer. 

 Assoc. Adv. Sci. vol. xxxii. p. 32 ; also Balfour's (Jonip. Embryol. 



