Mr. W. S. Kent on the Embryology of Sponges. 155 



Fig. 28. Two individuals of tlie same species about to coalesce. 



Figs. 29-33. Illustrating the coalescence or fusion of four individuals 

 of the same type, followed by the production of an irregular 

 amoeboid mass, which finally resolves itself by a process of seg- 

 mentation, and in a manner identical with that of the sponge- 

 monad and solitary collar-bearing form last figured, into a corre- 

 sponding morula-like body, the constituent units of which are 

 finally liberated as minute zoospore-like bodies which grow to 

 the parent form. Fi^s. 27 to 33, representative of this type, 

 are reproduced from Messrs. Dollinger and Drysdale's figures. 



Plate VII. 



Fig. 1. Amosha-Vike corpuscle or zooid of Halisarca lohularis, out of which, 



by repeated segmentation and differentiation of the cleavage- 

 masses, the characteristic spherical ciliated chambers or "am- 

 pullaceous sacs " are constructed, X 400 diameters. 



Figs. 2-4. Various phases of this process of segmentation, terminating at 

 fig. 4 in the production of a morula-like aggregation of rounded 

 blastomeres. 



Fig. 5, The succeeding developmental phase of the ampuUaceous sac of 

 the same sponge, as seen in optical section. The segment- 

 masses have now spread out upon the surface and assumed a 

 conoidal form, each of the same bearing apically a long lash- 

 like flagellum, which projects into the common spheroidal 

 cavity. 



Fig. 6. An example of about the same age, focussed superficially, in 

 which the segment-masses, while considerably separated from 

 one another, are held together by the hyaline or syncytium-like 

 wall of the body of the "sac," upon the inner surface of 

 which their apices project. 



Fig. 7. A fully matured ampuUaceous sac of the same sponge, as seen in 

 transverse optical section, and in which the previous conical, 

 uniflagellate segment- masses have developed into typical collar- 

 bearing sponge-monads or Spongozoa. The eversion of this 

 matured monad-chamber is alone required to produce a struc- 

 ture essentially con-esponding with the " swarm-gemmule " 

 represented at fig. 12 of the preceding Plate. X 800 diameters. 



Fig. 8. A few individual units or sponge-monads from the preceding 

 figure, further enlarged : n, nucleus or endoplast ; c. v, con- 

 tractile vesicle. 



Fig. 9. A colony of the independent, free-swimming, collar-bearing monad 

 Desmarella vwnilifurmis, S.K., which occurs in chain-like aggre- 

 gations of from two to as many as eight individuals, with 

 which the separated sponge-monads in the preceding figure 

 essentially correspond. X 1000 diameters. 



Fig. 10. Sporocyst-like bodies found associated with a siliceous sponge- 

 form {Halichondria, sp.). X 600 diameters. 



Fig. 11. Detached fragment of a siliceous sponge {Halichondria, sp.), 

 showing at a an ampuUaceous sac in its semideveloped or 

 moruloid condition, at 5 6 two amoebiform bodies emitting 

 pseudopodia, and which after assuming a quiescent or encysted 

 state, develop through the cleavage of their substance into 

 ampuUaceous sacs, sy, syncytium. Several typical adult 

 sponge-monads or Spongozoa are shown at c. 



