PORIFERA, CCELENTERATA, VERTEBRATA 75 



(2) Goette (1886) maintains that the gemmule con- 

 sists of cells from several germ layers ; (3) Carter 

 believed at one time that the gemmule was made 

 up of only one kind of cell ; and (4) several 

 authors (Marshall, 1884 ; Wierzejski, 1886 ; Zykoff, 

 1892; Weltner, 1892) believe that a number of 

 cells belonging to several classes are concerned in 

 the origin of the gemmule. 



Evans (1900) has described in detail the formation 

 and structure of the gemmules of Ephydatia hlemhin- 

 gia. In this species the first sign of the formation of a 

 gemmule is the presence of "single cells or groups 

 of cells scattered about chiefly in the dermal mem- 

 brane ; the strands of tissue which support the dermal 

 membrane ; and in the tissues situated immediately 

 below the subdermal cavity" (p. 89). No mitotic 

 figures were discovered in these cells and conse- 

 quently the reproductive part of the gemmule is 

 probably not derived from one mother-cell. These 

 cells wander "through the dermal membrane, and 

 strands of tissue which support the membrane, and 

 become aggregated in groups situated either deep 

 in the tissues of the sponge or even in the strands of 

 tissue above mentioned." 



Whether the reproductive cells of the gemmule 

 arise from a single cell by proliferation or represent 

 an aggregation without a common origin is still 

 unsettled, but the latter view is held by most in- 

 vestigators. If they do arise from a single cell, as 

 H. V. Wilson (1902) admits is a possibility, the 

 gemmule formation may be considered a kind of 



