SPERMATOGENESIS OF EUSCHISTUS Lat 
body, it occupies the long axis of the spermatid, and from now 
on may be termed the axial thread. This thread is now a fibril 
which in life exhibits no vibrations but is extended out straight 
from the cell, in marked distinction to the motile pseudopodium 
that will be described later; it has been drawn bent in figs. 121-126 
simply to save space in the drawings, but in life such bending is 
not seen. It would appear at this time to be of the nature of a 
skeletal rod to give firmness to the growing tail of the sperm. I 
have not drawn the whole tail of the sperm later than the stage of 
fig. 126 because it soon reaches a great length. But the axial 
thread can be recognized from this time up to the mature sperm 
(fig. 147) as a fine, deeply staining line extending from the head of 
the sperm backwards along the tail, enclosed in a mantle of 
mitochondrial substance. . 
In the stages of figs. 127-137 the centriole (c) is somewhat 
excentric; the axial thread is attached to one edge of it, on its 
opposite side lies the sphere (Sp). In figs. 121 to 125 the sperm 
is shown in dorso-ventral aspect, in lateral aspect in the other 
drawings. 
The centriole grows rapidly and becomes transversely elongated 
(figs. 124-137), and stains deeply throughout this period. Then 
it assumes a more irregular form (figs. 129, 131, 134, 136) as though 
it had divided into a plate of two or more smaller portions, but 
I have not been able to assure myself of the presence of distinct 
parts. Later it shifts the position of its long axis and penetrates 
somewhat into the nucleus (figs. 140, 141). Then it suddenly 
changes in appearance, showing one of two clear vacuoles, becom- 
ing very refractive; at the same time its appears constricted and 
pushes further into the nucleus (figs. 142, 143). In astage slightly 
later (fig. 144) a single, rather small, hollow centriole is seen within 
a clear space in the nucleus. In later stages (figs. 146, 147) no 
centriole can be found. It is difficult to interpret this sudden 
seeming disappearance of the centriole. The conditions of figs. 
142 and 143 would indicate that it is undergoing division, with 
a vacuole in each moiety. In the next stage the anterior portion 
would seem to have moved still further into the head. The other 
half may originate that lightly staining body placed in the head 
