PLA TE IX. 



EXPLANATION. 



FIG. 



1-12. HALISARCA DUJARDINII, Johnston sp. i, Spheroidal monad-chamber or 

 ampullaceous 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 ampullaceous 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 PL II. Fig. 30, x 1000 ; 

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

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

 4-11, progressive phases of development of an ampullaceous sac by segmen- 

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

 present the aspect of simple amoebiform 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 

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



13-17. HALISARCA LOBULOSA. 13 and 14, Detached ampullaceous 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-cells," x 400 (Metsch.). 



18-21. HALISARCA DUJARDINII. 18-20, Spheroidal cell-combinations, or rosette-gem- 

 mules, 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-gernmule, the externally projecting units possessing flagellate 

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

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



22-29. GRANTIA COMPRESSA, Bwbk. Swarm-gemmules or so-called ciliated larvae, 

 exhibiting various phases and modifications of development, as observed by 

 the author. 22 and 23, simple " planuloid " variety of such swarm-gemmule, 

 as viewed superficially and in longitudinal optical section, and shown in the 

 latter instance to be composed of similar closely apposed, conical, uniflagellate 

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

 swarm-gemmule, each constituent uniflagellate element being characterized 

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



