86 RICHARD EVANS. 



"as a simple ovum with modified form to meet the require- 

 ments of the case." 



It seems Carter was always uncertain as to the origin of 

 the gemmule, and at one time or another he appears to have 

 had four views. First, that the gemmule was a mere aggre- 

 gation of sponge-cells ; secondly, that it was an aggregation 

 of cells produced from one cell, the " ovi-bearing " cell ; 

 thirdly, that it was a single ovum, which was his final view ; 

 and fourthly, that it was a single " ovarium " of a dead 

 " spongozoon." 



In the year 1884 Marshall published an account of the de- 

 velopment of the gemmule of Spongilla lacustris (15). 

 He says that the first sign of the gemmule consists of a 

 number of amoeboid cells, which are found in the neighbour- 

 hood of the inhalant canals and the ciliated chambers, and 

 which he terms the " trophophores." They fill themselves 

 with reserve material, and wander together in groups. They 

 become round and give up water, so that they look like 

 masses of reserved food material. Very early round the 

 pseudomorula formed in this way there appears a delicate 

 structureless membrane, a cuticle, the matrix of which should 

 be probably looked for on the surface of the pseudomorula 

 itself. The "mesoderm" outside this cuticle builds at first 

 an endothelium which deposits on the cuticle further layers 

 of horny substance and delicate siliceous structures, in this 

 case spiny tangential needles. 



In the year 1886 appeared Goette's account of the develop- 

 ment of the gemmule of Spongilla fluviatilis (10). He 

 says that the first rudiment of the gemmule is formed by an 

 aggregation of ordinary parenchyma cells in a nearly spheri- 

 cal area of 36 — 44 fx in diameter ; really, the flagellated 

 chambers and canals of this region become enclosed in the 

 aggregation, which is produced through hypertrophy of the 

 cells. In this aggregation of cells the formation of two 

 layers quickly takes place; a central mass of cells, con- 

 taining a great number of yolk-granules, and an outer sheet 

 of cells, which become club-shaped and form a kind of 



