of Edinburgh, Session 1885 — 86 . 
807 
“ Stutzzellen,” the central part being simply the follicular cells 
altered by reagents. The spermatoblasts were explained away as 
misinterpretations of the temporary union of a number of spermato- 
cytes originating from the same parent spermatogonium. 
Helmann (1879) similarly described the division of each primitive 
cell into a mass of daughter-cells which are differentiated into 
spermatozoa ; while Krause referred the origin of the sperms to the 
indirect division of the (germinative) follicular cells, which form 
spermatogemmae (or Knauelzellensaule) of “spermatoblasts,” while 
the nucleated basal portion forms the “spermatogonium.” With 
this Meyer (1880) also agreed, regarding the. follicular cells of Yon 
la Yalette St George as the earliest stages of the spermatogonia and 
spermatogemmae. Nussbaum’s well-known memoir on the differentia- 
tion of the sex-elements contained an account of spermatogenesis, 
which substantially agreed with that of La Yalette. From the primi- 
tive male ovule, spermatogonium and follicular cells both arise, as in 
some cases of oogenesis ; by indirect division within the spermato- 
gonium, cells are formed which become spermatocytes, though a few 
peripherally situated probably form a second enveloping membrane 
- — the “ Cysfeenhaut.” 
It is most convenient, at this stage, to refer to the spermatogenesis 
of Invertebrates, which has also been the subject of numerous 
important researches, together comprehending almost every group. 
It is only necessary to allude to a few of these. In 1877 F. E. 
Schulze described the spermatogenesis of the sponge Halisarca, in 
which germinal mesoderm cells, analogous to those which give rise to 
ova, divide repeatedly to form morula-like masses, composed of about 
thirty cells, each of which develops into a spermatozoon. Found 
the larger clumps, a mesoderm capsule of flat polygonal endothelial 
cells is formed, as round the ova. An interesting observation on 
the spermatogenesis of Sycandra raphanus is due tu Polejaeff (1882), 
who described the nuclear division of the primitive amoeboid cell, — 
the smaller half forming a cover cell ( Deckzelle ), which embraces the 
sperm- cells resulting from the repeated division of the larger half 
(the Ursamen-zelle )„ 
In 1844 Meckel had described the spermatozoa of the snail, as 
arising superficially from a mother-cell, and this view had been 
confirmed by various authors. According to Duval, the mother-cell 
