The spermatogenesis of Hydra. 397 
no indications of chromomere swellings (Fig. 16). Whether it seg- 
ments by the same method of formation of the spiral whose half 
turns became meridional I have not been able to determine, but I 
think not, for I have searched diligently for such stage without 
finding it, while the spireme of the spermatogonia within the sper- 
mary as given in Fig. 35 is very conspicuous. After the thread had 
fragmented, however, we find twelve V-shaped chromosomes arranging 
themselves in a equatorial plate (Fig. 17). In Fig. 18 the upper 
part of the cell has been partly cut away and one is looking down 
into the lower half, the pole of which is tipped toward the observer. 
Each V-shaped chromosome contains four chromomeres. Now the 
division is a longitudinal division, beginning at the tip of the V’s 
where the mantle fibres attach. The ends of the daughter V’s 
however often seem to hang to each other with tenacity, so that 
the chromosomes are changed to rod-shaped bodies during the meta- 
phase. Moreover the half-chromomeres produced by the longitudinal 
splitting of the chromosomes seem to fuse now so that each rod- 
shaped chromosome contains four chromomeres. This process is not 
universal, however, for sometimes we get in the spermatogonia 
(recognized by their size) a persistence of the open V’s until their 
fusion in the daughter nuclei (Fig. 21). And this seems to be the 
almost universal method of division in the interstitial cells. 
Mitosis in interstitial and ectoderm cells. 
The division of the interstitial cells and as far as observed of 
the ectoderm cells when they divide mitotically is as follows: — 
The cell consists of an indistinct reticulum in the meshes of which 
is the cytolymph. Similarly the nucleus is made up of a mesh work 
of fibres containing in their interstices the karyolymph and supporting 
one or more, usually one nucleolus. 
Prophase. 
The first indication of approaching division is the increased 
intensity of stain which the reticulum assumes, especially in the 
nucleus. The nucleolus then fragments into two or more spherical 
granules, which gradually disappear. Contemporaneously the fibres 
of the reticulum become coarser, and at their intersections the 
microsomes are prominent. This process goes on, the fibres and 
microsomes becoming fewer until the linin fibres are very coarse 
and the microsomes large and deeply staining. At last all the linin 
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