400 E. R. Dowxixe, 
The cell generations. 
It has been exceedingly difficult to make out the cell generations. 
The growth of the spermary is so rapid and the spermary like the 
other tissues of Hydra is so mobile that the cells are of a great 
variety of shapes. Moreover there is not a succession of zones in 
the spermary corresponding to the cell generations as in many of 
the higher animals, but a bunch of spermatogonia may be retarded 
in their development until they get well out toward the tip, or 
they may develop precociously so that there will be spermatocytes 
and spermatids down among the spermatogonia. It was a few 
fortunate cases of the former character where spermatogonia of the 
first generation had been retarded in development until reaching 
the outer zone of the spermary that enabled me to determine with 
definiteness the number of cell generations, for but here they were 
released from pressure, assumed consequently a spherical form, and 
this makes measurement of the successive stages easy. From the 
first measurements of cells, in the deeper parts of the spermary, 
I was persuaded that only one generation of spermatocytes was 
present, and so reported the matter. It was hoped that some such 
simplification of the process of spermatogenesis would be found in 
this lowly form; but later and more favorable measurements have 
convinced me that there are really two generations of spermatocytes. 
Measurements will be tabulated later. 
Mitosis in the spermatocytes of the first order. 
When the spermatogonia divide, the daughter nuclei are spheroids 
with the centrosome above one pole (Fig. 39). In the early stages of the 
spermatocyte of the first order, — that is, after division of the 
spermatogonia is completed, — the shape of both cell and nucleus 
changes, becoming elongated in an axis, parallel to the plane of 
division of the spermatogonia. The centrosome then lies at one end 
of the cell’s long diameter instead of in a short diameter. The 
chromomeres of the nucleus persist and without going into a reticu- 
late condition they become connected into a beaded thread, at first 
irregularly twisted, but finally spirally coiled on the nuclear walls. 
The cell is now a flattended polyhedron. The nucleus is an ellipsoid 
of revolution with its major axis coinciding in direction with the 
major axis of the cell. The axis about which the spireme is coiled 
is the major axis of the nucleus (Fig. 43). The persistent centrosome 
