SOME PROBLEMS OF REPRODUCTION. 49 
and the spermatozoon is amceboid.! By the passage of seg- 
mentation to budding we have a transition to mode (6). 
According to Ebner,? in the Rat each spermatogonium 
divides into four spermatocytes; and a number of the broods 
so formed contract a syncytial union with an attached and 
uninucleated cell (Sertoli’s cell), which thus plays the part of 
a nurse to numerous spermatozoa. 
(6) The second mode of spermatogeny is that fully studied 
by Blomfield in Lumbricus. Here the nucleus of the sper- 
matogonium undergoes repeated divisions; the brood nuclei 
come to the surface of the apocytium so formed and pass into 
cytoplastic buds, whose ends finally taper into flagella. These 
uninucleate buds are ultimately, as spermatozoa, abstricted 
from a central residue of non-nucleated cytoplasm, the ‘‘ blas- 
tophore” of Blomfield. It is uncertain whether a cytoplastic 
blastophore is left in all cases of spermatogeny by budding ; 
and the differentiation in this case from mode (a) is difficult. 
Comparing the holoblastic and the centrolecithal ova, the 
segmentation of the zygote in Euflagellates and in Nocti- 
luca, we can fully realise of how little general import, phy- 
siological or morphological, is the presence of the non-nucleated 
blastophore. 
(c) The third mode of spermatogeny occurs in the Sponge 
Grantia (Sycandra),? the Molluse Helix, and some Verte- 
brates. Here, at an early stage of gametogenic fission (at the 
first bipartition in sponges), one nucleus undergoes no further 
divisions, and can only have a nutritive (or protective) function 
henceforward. In most cases the spermatogonium is attached 
by the basal cytoplasm in which this nucleus lies; the other 
nuclei pass to the free end of the cell, and henceforward sper- 
1 We may correlate the absence of a flagellum here, as in most Arthropods 
also, with the absence of cilia in the tissue-cells, and the complete chitinisa- 
tion of the body. 
2 «* Spermatogenese bei Saugethieren,” in ‘ Arch. f. mikr, Anat.,’ xxi, p. 236. 
Unfortunately Ebner’s views are contested, and the matter is unsettled. 
8 And in Spongilla fluviatilis; see R. Fiedler, “Ueb, Hi- und Samen- 
bild. bei Spongilla fluviatilis,” in ‘Zeit. f. Wiss. Zool.,’ t. 48. In this 
group the ‘nutritive cell’ forms an investment to the brood of spermatocytes. 
VOL. XXXIII, PART I.—NEW SER. D 
