512 



WILSON. 



[Vol. V. 



The increase in size of the gemmule takes place by means of 

 cell growth and division, and by the fusion of neighboring 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 occurrence of such an origin for gemmules 

 I may say, that after looking over a great number of prepara- 

 tions, 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 strik- 

 ing change in its structure, until it is nearly as large as the 



At 



^\\ 



Fig. i. Portion of Esperella mesoderm, showing two gemmules, g and g', each 

 surrounded by follicle of flattened cells, g is a very young gemmule; g 1 , consider- 

 ably older; c. w. = canal wall; f.c — flagellated chamber. 



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

 ripe gemmule. The ripe gemmule is spheroidal and is made up 

 of cells so closely packed and so filled with fine yolk granules 

 that the cell boundaries are indistinct. The nuclei of the cells 

 are very small. During the growth of the gemmule the sur- 

 rounding tissue becomes largely incorporated in the follicle ; and 

 whereas the gemmule in its early stages lay in the mesoderm 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 gemmule next undergoes a process 

 which presents a superficial analogy to segmentation. The 



