237 
Development of Pyrosoma. 
question for the Tunicates in general cannot be regarded as 
having been exhaustively worked out. 
1. The Kalymocytes of the Ovum of Pyrosoma and their 
Function in the Development of the Cyathozooid . 
So far as I am aware, Kowalewsky was the first to observe 
the occurrence of kalymocytes in the ovum of Pyrosoma. 
Kowalewsky terms them u inner follicle-cells,” but recog- 
nizes their homology with the so-called test-cells of the 
Ascidians. He also described the mode of origin of these 
cells with perfect accuracy, and shows that they are nothing 
else than follicle-cells which have separated from the follicle- 
wall and wandered into the space between the latter and the 
surface of the yolk. From Kowalewsky’s figures we can at 
once see that the kalymocytes inner follicle-cells,” Kow.) 
differ in form and structure from the true follicle-cells. As a 
matter of fact these cells differ so much from the blastomeres, 
not in form and structure only, but also in the way in which 
they are affected by staining-reagents, that, even with a low 
power, they can be very easily recognized in stained prepa- 
rations. 
The kalymocytes appear in the ovum of Pyrosoma at a 
very early stage, and are to be observed in tolerably large 
numbers even before the commencement of segmentation. 
With reference to their origin, I can completely confirm 
Kowalewsky’s statements ; different stages in the separation 
of these cells are very easily made out in sections. As regards 
the structure of these cells, however, Kowalewsky is not 
altogether accurate. This is explained by the fact that 
Kowalewsky underestimated the role of the kalymocytes, 
and therefore pays them less attention than they actually 
deserve. The structure of the kalymocytes is very charac- 
teristic, although their form varies according to the place in 
which they are found. They are to be met with in different 
parts of the ovum — immediately beneath the wall of the 
follicle, in the interior of the yolk, or between the blasto- 
meres, and they are everywhere distinguished by a different 
shape, corresponding with their situation. The cells found 
at their place of origin have a primitive shape, which we may 
regard as typical. They are pyriform, tapering at one pole 
and widened at the other. Each cell contains within its 
tapering portion a nucleus, which, owing to the readiness with 
which the protoplasm takes a deep stain, is not very con- 
spicuous in coloured preparations. The nucleus is vesicular, 
