818 Proceedings of the Royal Society 
cells probably result from a primitive cell with morula-like division 
of its nucleus, as bas been repeatedly observed in oogenesis. A 
more intimate parallelism is suggested by the comparison repeatedly 
proposed, with a measure both of morphological and physiological 
probability, between the polar cells of the ovum and similar bodies 
occurring at various stages in spermatogenesis.* In the use of 
terms like sperm-morula, sperm-blastula, &c„, Balfour and others 
have dimly suggested the further comparison between the division 
of the sperm-mother-cell (S 1 ) and the segmentation of the ovum. 
This comparison it is one of the objects of this paper definitely to 
formulate, collating various modes of spermatogenesis with apparently 
homologous modes of segmentation. 
The unification is sought by comparing the manifoldness of 
spermatogenesis to the manifoldness of segmentation, for as the seg- 
mentation of the ovum is varied, the same is not a 'priori impossible 
in the segmentation of the male ovule. These two sets of pheno- 
mena, in regard to which our knowledge has progressed separately 
through empirical evolution, seem to have in short the same mor- 
phological and physiological rationale. This comparison hinted at 
in the nomenclature of Balfour and others, has also been proposed 
by Herrmann (1881): — “The division of the male ovule into a 
series of generations of daughter cells forming spermatoblasts, is a 
phenomenon comparable to that exhibited by the ovum in the for- 
mation of the blastoderm. The cellular individualisation occurs by 
segmentation (in most ova, and for instance in the male ovules of 
Selachians), or by superficial germination (in the ova of Arthropods 
and in most male ovules), or by other mechanism, always, however, 
fundamentally of the same nature. It seems then more important 
to determine exactly the mechanism of division than to give a 
particular name to each stage of segmentation.” 
Such suggestions have, it seems to us, great value; the comparison 
must, however, be developed in detail, (a) In such a simple case of 
spermatogenesis as that illustrated by sponges, where a cell dif- 
ferentiated from the mesoderm divides up into a regular sphere of 
uniform cells, each an incipient spermatozoon, or where this occurs 
with the interesting specialisation of one of the two first halves to 
* Cf. J. Arthur Thomson “On Recent Researches on Polar-Cells,” &c., in 
Quart. Jour. Micr. Sci. (1886). 
