108 KIOHARD EVANS. 



PLATE 4. 



Fig. 14 (x 130). — A representation of a stage slightly later than that 

 sliown in Fig. 13. Note that the columnar layer is complete, and that the 

 loose membrane which surrounds the gemniule is almost complete and is con- 

 nected by strands of tissue, in which ainphidiscs are found, with the general 

 sponge structure. Further, note that there are neither amphidiscs nor 

 trophophores among the columnar cells. 



Fig. 14« (X 9fiO). — A representation, more highly magnified, of a portion 

 of the columnar layer and loose membrane shown in Fig. 14. 



Fig. 15 (X 130). — A representation of a stage slightly later than that 

 shown in Fig. 14. Note that there are amphidiscs {amphi.) over half the 

 extent of the columnar layer of cells, while the other half is as yet free of 

 them. Also note that the inner chitinous layer is still incomplete at the 

 point where the pore will be formed; but the yolk granules in tiie interior 

 are fully formed. The outer end of the amphidiscs extends beyond the 

 columnar cells. 



Fig. 15« (x G65). — A representation, more highly magnified, of the amphi- 

 discs (ampAid.) lying inside the modified scleroblast {mod. sclerob.) which has 

 lost its nucleus, and of the columiKir cells lying between the amphidiscs. 

 Note that the inner ends of the columnar cells are becoming clear, as is sliown 

 in Fig. 15. 



Fig, 156 (x 6G5J. — .\ representation of the inner chiiinous layer {in. chit. 

 lay.), the columnar layer {col. cell.), the loose membrane, and one of the 

 strands which pass to the membrane, the whole being taken from the region 

 intermediate between the one occupied by amphidiscs and the one devoid of 

 them in a gemmule similar to that shown in F'ig. 15. Both amphidiscs are 

 shown inside their scleroblast s, and the one in the strand of tissue outside is 

 being carried to its position alongside the other amphidisc among the columnar 

 cells. 



Fig. 1G (X 130). — A representation of a stage slightly later than that 

 shown in l^ig. 15. Note that l.lie s[)icular layer and the inner chitinous layer 

 are complete. Further, note that the columnar cells have passed ont and are 

 situated externally to the outer end of the amphidiscs, their inner ends having 

 been modified to form the parenchyma-like substance situated between the 

 amphidiscs. 



F^ig. 10« (x 6G5). — A more hii,'hly magnified representation of the gem- 

 mule coat shown in Fig. 16. Note that the columnar cells are forming the 

 outer chitinous layer and are becoming separated preparatory to their passing 

 back to the sponge. 



Fig. 17 (x 130). — A representation of the fully-developed gemmule, show- 

 ing the contents passing up the pore as far as the chitinous septum {chit. 



