A. Hyatt — Larval Theory of the Origin of Tissue. 335 



The adult condition of Budorina or Yolvox in other words is 

 a permanent morphological equivalent of the blastula stage in 

 the ovum of a Metazoon, and a spermatocyst 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 sperma- 

 tozoa also which are produced by fission of the nucleus resem- 

 ble the young of the Amcebinaa 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 functionally 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 egg, and forcing their way into the vitellus. 

 Ultimate union with the female nucleus of the ovum by pas- 

 sage through the vitellus is quite distinct. It has appeared to 

 us to be like concrescence in low forms an exhibition of mutual 

 attraction which indicates affinity, and like all sexual processes 

 a vital attraction 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 pre- 

 paratory to reproduction by division as among Myxomycetes. 

 Crinkowski 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. Mik. Anat., vol. ix). 



There is a gradation in the stages of development of the 

 ectoderm, endoderm and mesenchyme in the sponges which 

 show they have retained the ancestral protozoonal character- 

 istics in some cells more than in others. Thus the ectodermic 

 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 only lo- 

 cally on the walls of the archenteron in the intervals between 

 the diverticula (primitive ampullae)."* 



In the mesenchyme of sponges the cells have been subjected 

 to fewer changes and they preserve their ancient amceboidal 

 forms unaltered. The comparatively great change in the evo- 

 lution of the group probably took place after the transfer of 



* Von Lendenfeld (Austral. Sponges, vol. ix, pi. 4, Proc. Linn. Soc. N. S. "Wales, 

 pi. 64-65), describes Homoderma sycandra as having these cells equally distributed 

 all over the endoderm as well as in the siDgle ampullae. 



