570 MR H - D - s - GOODSIR ON THE DEVELOPMENT, STRUCTURE, AND 



off between the tubular membrane and peritoneum, shewing the first mode of generation ; D gem- 

 mules being developed in the subserous tissue, shewing the other mode of generation ; E gemmules 

 of the second mode farther advanced ; F burst from their nidus through the peritoneum, and have 

 obtained a covering of the tubular membrane. 



O 



Fig. 3. Thin transverse section of abdominal parietes, very much magnified, shewing blood globules, and 



ovules of Diskostoma in the subserous tissue. A peritoneum ; B blood globules ; C gemmules of 



solistoma. 

 Fig. 4. Internal surface of the vesicle of Acephalocystis simplex, with numerous young ones of various 



sizes being developed and thrown off. 

 Fig. 5. Group of Diskostoma acephalocystis dependent from the omentum. A omentum ; B B young 



of the Diskostomata ; C peritoneum, forming walls of the peduncular cavity; DD peduncle; 



E E Adult specimens of Diskostoma ; F external membrane. 

 Fig. 6. Section of the vesicle of Acephalocystis simplex, very much magnified, shewing three cells or 



young ones lying between the membranes. 

 Fig. 7. Tooth of Csenurus cerebralis. 

 Fig. 8. Scutella. 

 Fig. 9. Triotoma. 

 Fig. 10. Lerononeme, monilaris. 

 Fig. 11. Echinorynchus, balanarum. 



PLATE XVI. 



Fig. 1 . Ovule of Csenurus cerebralis, first stage. A external covering or shell ; B membrane of yelk ; 

 C membrane of germinal vesicle ; D germinal spot ; E clear central space. 



Fig. 2. Second stage of ovule of Csenurus. A shell ; B membrane of yelk ; C germinal vesicle ; D ger- 

 minal spot enlarged ; E clear space. 



Fig. 3. Third stage of ovule. D germinal spot nodulated ; E clear space enlarged. 



Fig. 4. Fourth stage of ovule. D germinal spot has thrown off the nodules, which have become cells ; 

 E central cell ; F germinal spot for the second generation of cells ; G clear central space. 



Fig. 5. Fifth stage of ovule. C primary germinal vesicle ; D primary circle of cells ; E central cell of 

 primary circle of cells become larger ; F its nucleus, become larger and nodulated. 



Fig. 6. Sixth stage of ovule. A external covering or shell ; B membrane of yelk, with probably the 

 primary germinal vesicle, which has been distended, lying underneath it or within it ; C primary 

 circlet of cells ; D central cell of primary circlet very much distended ; E secondary circlet of cells, 

 not yet finally formed ; F central cell of secondary circlet ; G its nucleus and accompanying clear 



Fig. 7. Ovule of Csenurus cerebralis considerably advanced in the discoidal period of development ; 

 A central productive nucleus. 



Fig. 8. One of the first stages of the vertical period of development of ovule. A primary series of 

 stages in the discoidal period ; B secondary series in the discoidal period ; C cells of the vertical 

 period ; D D D productive centres ; E central nucleus of one of the centres. 



Fig. 9. Ovule of Canurus, very far advanced in the discoidal period of developement. The concentric 

 circlets of cells are seen ; and the central circlet near to the lower edge as it was pressed between 

 the plates of glass, shewing that there is elevation, to a certain extent, during the latter stages of 

 this period. A external covering of gemmule ; B some of the concentric circles of young cells ; 

 C central cell of last formed circlet ; D its nucleus and clear space. 



