514 W. B. HARDY. 



fragments may sometimes be seen ; and further because the 

 muscular elements are absorbed for some little space about the 

 point where the rupture takes place (figs. 7 to 10). 



The tongue of endoderm-cells rapidly becomes a tubular 

 outgrowth, and the cells at its apex lose their nutritive 

 spheres and become small, dense, on the whole ill-staining 

 cells. 



At this stage it is perhaps impossible to distinguish the limit 

 between ectoderm and endoderm, while at the same time a 

 fusion of cell substance has taken place (fig. 10), so that we 

 have a stage closely resembling the blastema which gives rise 

 to the bud as described above. 



Fig. 10 represents this stage, and is an accurate drawing, 

 made with the aid of a camera lucida, of a preparation 

 from a specimen killed with corrosive sublimate and stained 

 with picro-carmine; the whole specimen being remark- 

 able for the good preservation and clear definition of its 

 histological elements. The section figured passes rather 

 obliquely through the young gonophore, but the next in the 

 series shows that the primitive germ-cells have now travelled 

 in under the superficial columnar cells of the ectoderm to form 

 a cap for the fused ectoderm and endoderm. 



The next stage to be noticed is in many respects remarkable. 

 By a fresh formation of supporting lamella the whole bud with 

 its contained germ-cells becomes separated from the maternal 

 tissue, while at the same time a fold of supporting lamella be- 

 comes formed which separates the ectodermal elements with 

 the primitive germ-cells from what is usually known as the 

 endoderm lamella (fig. 11). The endoderm lamella, there- 

 fore, from this time onwards, is separated from the endo- 

 derm of the parent by a well-defined and permanent support- 

 ing lamella ; and it is noticeable that up to this stage and until 

 they degenerate the cells of the endoderm lamella are not of the 

 ordinary endoderm type, but resemble in every detail 

 the ectodermal cells of the gonophore.^ 



* The columnar cells of the maternal ectoderm remain undisturbed and 

 unaltered by these various changes. I regard them as belonging to the 



