ELISHA MITCHELL SCIENTIFIC SOCIETY. 97 



and forming a follicle. The gemmule, as thus formed, is 

 at first quite small, often showing not more than five cells 

 in section, though a considerably larger gemmule may 

 be directly formed from a group of cells. The cells 

 of the gemmule, once the follicle is formed, are very 

 closely packed. 



The increase in size of the gemmule takes place by means 

 of cell growth and division, and by the fusion of neigh- 

 boring small gemmules. The latter process throws into 

 shade the seemingly important question, Does a gemmule 

 ever start as a single cell ? In regard to the actual occur- 

 rence of such an origin for gemmules, I may say that, 

 after looking over a great number of preparations, my 

 conclusion is, that perhaps a little group of mesoderm 

 (gemmule) cells is so derived in very rare instances, but 

 the case occurs so seldom as not to be worth consideration. 



The gemmule continues to increase in size, without any 

 striking change in its structure, until it is nearly as large 

 as the swimming larva. In this condition it may be spoken 

 of as the ripe gemmule. The ripe gemmule is sphe- 

 roidal and is made up of cells so closely packed and so 

 filled wnth fine yoke granules that the cell boundaries 

 are indistinct. The nuclei of the cells are very small. 

 During the growth of the gemmule the surrounding tis- 

 sue becomes largely incorporated in the follicle; and 

 whereas the gemmule in its early stages lay in the meso- 

 derm of the sponge, in its ripe condition it lies in one 

 of the larger canals, suspended by strands of tissue which 

 now bind the follicle to the canal wall. The ripe gem- 

 mule next undergoes a process which presents a super- 

 ficial analogy to segmentation. The solid gemmule splits 

 up into irregular masses of cells. These continue to split 

 up into smaller and smaller masses, the gemmule mean- 

 while increasing in size, owing to the absorption of fluid, 

 so that the several masses of cells are distinctly separated 

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