P LA TE IX. 



EXPLANATION. 



Fig. 



I-I2. Halisarca Dujardinii, Johnston sp., vol. i. p. i88. — i, Spheroidal monad- 

 chamber or ampuUaceous sac, as seen in optical section without intersecting 

 an afferent or efferent aperture, X 800; the introversion of this monad-chamber 

 is alone required to produce a rosette-gemmule or ordinary swarm-gemmule as 

 delineated at Figs. 20, 24, and 25 ; 2, six laterally attached collared monads 

 from an ampuUaceous sac of the same sponge, these corresponding remark- 

 ably in their isolated condition with the moniliform colonies of the collared 

 monad Desmarella moniliformis represented at PI. II. Fig. 30, x 1000; 

 3, ampuUaceous sac of the same type as seen in optical section, and inter- 

 secting, where indicated by the arrows, an afferent and efferent aperture ; 

 4-1 1, progressive phases of development of an ampuUaceous sac by segmen- 

 tation from a primitive amoeboid body, X 400; at 10 the segmented products 

 present the aspect of simple amcebiform corpuscles possessing no flagellate 

 appendages, and held together by intervening hyaline cytoblastema ; at 12 

 the same elements closely approximated have developed internally-projecting 

 flagella, but still want the characteristic collars ; 12, profile view of matured 

 ampuUaceous sac, with surrounding cytoblastema ; at c, enclosed cytoblasts. 



13-17. Halisarca lobulosa, vol. i. p. 189. — 13 and 14, Detached ampuUaceous sac, 

 X 400 (after Metschnikoff) ; 15-17, subspheroidal, freely detached cell- 

 aggregations, with externally-projecting flagella, as figured and described by 

 Metschnikoff under the title of " rosette-ceUs," x 400 (Metsch.). 



i8-2r. Halisarca Dujardinii, vol. i. p. 190. — 18-20, Spheroidal cell-combinations, or 

 rosette- gemmules, more fully developed, as observed by the author, and shown 

 to consist of various numerical aggregations of typical collared monads, x 800; 

 21, portion of the same sponge with, at a, earlier and undetached condition of 

 a similar rosette-gemmule, the externally projecting units possessing flagellate 

 appendages, but as yet no collars ; at b, portion of an adjacent ampuUaceous 

 sac ; c, c, cytoblasts immersed within surrounding cytoblastema, x 800. 



22-29. GraNTIA COMPRESSA, Bwbk., vol. i. p. 1 78. Swarm-gemmules or so-caUed ciliated 

 larvae, exhibiting various phases and modifications of development, as observed 

 by the author. — 22 and 23, simple " planuloid " variety of such swarm-gem- 

 mule, as viewed superficiaUy and in longitudinal optical section, and shown in 

 the latter instance to be composed of similar closely apposed, conical, uniflagel- 

 late elements, x 350 ; 24, portion of longitudinal section of a more advanced 

 swarm-gemmule, each constituent uniflagellate element being characterized 

 by the possession of a distally developed rudimentary collar, which embraces 



