810 
Proceedings of the Royal Society 
The researches of Jensen on the spermatogenesis of numerous 
invertebrate forms, were mainly corroborative of the views of La 
Yalette St George. A spermatogonium divides into a mass of sper- 
matocytes, or a spermatogemma, which includes a distinct, sometimes 
nucleated cytophore (sperm blastophore). This is regarded, how- 
ever, not as a separated off portion of the mother-cell, but as the 
result of the internal destruction of the central spermatocytes, or 
of those nearest the ampulla wall. 
In the recent account of the spermatogenesis of Ascaris megalo- 
cefhala given by Yan Beneden and Julin, primitive male ovules or 
“ spermatomeres,” form, by direct division, spermatogonia • each of 
the latter divides indirectly into four spermatocytes, which together 
form a spermatogemma. Each spermatocyte forms a cytophoral por- 
tion towards the centre of the spermatogemma, and these four portions 
compose the so-called cytophore, from which the spermatozoids are 
liberated. This recent research is of further interest, though this does 
not specially concern us here, for the description of a process, observed 
in the formation of the spermatogonia, which exactly corresponds 
with the account of polar cell formation given by Yan Beneden. 
One of the clearest accounts of invertebrate spermatogenesis is 
given by Yoigt in regard to Branchiobdella , in which the following 
five stages are distinguished — (1) sexual cells, (2) spermatogonia (or 
Stammsamenzellen), (3) spermatocytes (or Samenvermehrungszellen), 
(4) spermatides (or Samenausbildungszellen), and (5) spermatozoa 
(or Spermatosomen). The first are the embryonic cells, the second are 
the homologues of the ova and the origin of a sperm-bundle, the 
third form collectively a spermatogemma, the fourth are not yet 
perfectly differentiated sperms, nor freed from the separated-off por- 
tion of the spermatocyte. The same nomenclature is followed by 
Platner in his recent account of Pulmonate spermatogenesis. The 
spermatogonia are at an early stage the only cells in the herma- 
phrodite gland besides the ova. They divide indirectly to form 
spermatocytes, but a large proportion of them persist, arranged in 
pillars between the spermatocyte groups, and subsequently form not 
only a new generation of spermatocytes, but also new “ basal cells,” 
after the others have disappeared. These basal cells appear at an 
early stage adjacent to the alveolar wall, and resemble spermato- 
gonia, though they never divide, but merely serve as centres, round 
