SUTTON : SPERMATOGONIAL DIVISIONS IN BKACHYSTOLA MAGNA. 143 



the colls upon one side, in the nietaphase, for instance, and those on 

 the other side in a middle or late telophase, and nowhere any inter- 

 mediate stages. Such an instance is shown in fig. Gr, and here, as it 

 generally happens in these cases, may be .seen in the middle, between 

 the two kinds of cells, one (fig. 40) which, by its poverty of chroma- 

 tin and the peculiar brownish cast of the same, as well as by the 

 cloudy aspect of its cytoplasm, shows itself to be degenerating. 



These degenerating cells are primary spermatogonia, and the rea- 

 son for their presence here and for their degeneration is probably as 

 follows : Two neighboring primary spermatogonia pass through the 

 transformation division and reach, say, the two- or four-cell stage, and 

 at this time have between them another primary spermatogonium. 

 The next division greatly increases the volume of these two cysts and 

 their walls meet around the cell between them on all sides. Then, for 

 some reason, the contiguous ])ortions of the cyst membranes are re- 

 sorbed, the two cysts become united, and the cell in question is impris- 

 oned in the middle of what is now a single cyst. There, being cut off 

 from the structures from which it has been wont to derive its nourish- 

 ment, it rapidly breaks down and disappears, and is never found in a 

 cyst of more than twenty cells. 



In cases of this kind, where, on account of their different origin, 

 the cells of a cyst re^) resent two different stages of development,, the 

 tendency is for the one set to go slower or the other faster, so that in 

 the course of a few divisions they get in step, as it were, with one an- 

 other. 



This union of young cysts accounts for the fact that occasionally 

 we find, in the zone of spermatocytes, cysts of exceptionally large size, 

 while in general they are of about equal volume, indicating a fixed 

 number of spermatogonial divisions. 



The question now arises. How from a single cell and its cell mem- 

 brane do we get two cells each with its cytotheca, and in addition a 

 cyst membrane containing both these daughter-cells V The solution 

 seems to be this : In the early stages there is between and among the 

 primary spermatogonia a membranous intercellular substance with 

 which they are in intimate relation, as shown by the fact that they 

 never shrink away from it. As development jjroceeds, however, the 

 close relation between the cell and intercellular substance is lost, and 

 in the metaphase (as was the case with the cell shown in fig. 10 and 

 also in fig. D) we sometimes find the cell membrane separated in 

 places from its capsule, {a, fig. D.) 



It now only remains for the separation to become complete. When 

 the two-cell stage is reached the spermatogonia and the cyst which 

 contains them are independent structures. As the number of cells 



