8» KIGHAKD EVANS. 



of mesencliyme cells of the sponge. The peripheral cells be- 

 come club-shaped and not columnar. This change takes place 

 gradually^ not all at once. The club-shaped cells secrete the 

 inner cuticle, and the amphidiscs migrate from the sponge 

 and take up their position among the club-shaped cells, which 

 subsequently migrate outwards, secrete the outer cuticle, and, 

 finally losing their club-shaped form, gradually become re- 

 sorbed. 



In the year 1893 Weltner published a short paper (18), in 

 which he brings together the different views expressed as to 

 several important points in connection ^vith the structure and 

 development of the gemmuie, and from his own observations 

 draws his own conclusions. Having discussed the use of the 

 protective coat ; the presence of a thin membrane, which he 

 does not believe to exist, round the reproductive portion of 

 the gemmuie ; the number of nuclei in each cell, of which he 

 has seen more than one in several cases, he finally deals with 

 the question of the origin of the cells of the gemmuie, in the 

 first rudiment of which he finds three kinds of cells, namely 

 cells which have yolk-bodies alone, cells which display fine 

 granules of equal size and a distinct nucleolus, and cells 

 Avhicli have large granules of unequal size. The third class 

 of cells are dilferent from the cells with granules of unequal 

 size found in the parenchyme. 



He comes to the conclusion that the development of the 

 gemmuie is not yet sufficiently known, and that a fresh 

 inquiry should be instituted as to two main points : first, 

 the orip'in and nature of the cells which form the first rudi- 

 ment of the gemmuie ; secondly, to ascertain the fate of 

 these cells. 



He suggests that their origin and nature should be exa- 

 mined wath a view to the following possibilities : 



Is the first rudiment of the gennnule formed from a single 

 cell which has the value of an egg ? Then the gemmuie 

 should be a group of segmenting cells. 



Or, does the inner mass of the gemmuie arise from one class 

 of cells derived from the previous mesoderm ? 



