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



Fig. 11. Optical section of a portion of a still further advanced condition 

 of the same swarm-gemmule, in which rudimentary collars have 

 been developed around the distal flageUa ; through the enlarge- 

 ment and expanding outward of the cellular constituents a central 

 cavity is now possessed by the common body. 

 Fig. 12. The fully matured condition of the same swarm-gemmule, which 

 is now shown to be an ovate aggregation of typical coUar- 

 bearing monads similar to that represented at fig. 1, and of which 

 the parent sponge-stock is essentially composed. 

 Fig. 13. Separated monads from successive developmental conditions of a 

 similar swarm-gemmule, that at a possessing a flagellum only, 

 and the other, h, being provided -ndth its characteristic collar, 

 contractile vesicle, and endoplast. 

 Fig. 14. Adult and immature conditions of a solitary collar-bearing flagel- 

 late monad, Monosiga angustata, S. K,, — a representing the col- 

 lar less and immature one, h the adult form, and both exhibiting 

 a remarkable correspondence with the similar developmental 

 phases of the isolated sponge-monads given in the preceding 

 figure, X 2500 diameters. 

 Fig. 15. An irregularly-formed acom-shaped'swarm-gemmule from the same 

 sponge, in the anterior part of which the monads have not yet 

 developed their coUars, while at the posterior end the collars and 

 flagella have been withdrawn, and the separate monads, coales- 

 cing laterally with one another, accompanied by the exudation 

 of a syncytial film, have produced anamorphous amoeboid mass. 

 Fig. 16. Another example of an "acorn-shaped" swarm-gemmule from 

 the same sponge, in which the disparity of development between 

 the constituent monads of the anterior and posterior halves is not 

 so considerable ; those of the latter present the characteristic 

 adult collar-bearing form, while those of the anterior portion 

 possess as yet only single terminal flagella. 

 Fig. 17. An irregular nest-shaped swarm-gemmule from the same sponge, 



composed of adult coUar-bearing monads. 

 Fig, 18. An abnormal and entirely imsymmetrical swarm^emmule from 

 the same sponge-form, in which the constituent monads exhibit 

 the two phases of development presented at fig. 15. 

 Figs. 19, 20. Two swarm-gemmules of HaUsarca lobnlaris, in the first of 

 which the as yet immature and uniflagellate monads correspond 

 with each other in size, while in the second those of the lower 

 portion are considerably more developed (after Barrois). 

 Fig. 21. Adult monad of the solitary coUar-bearing loricate type Salpin- 

 gceca fmiformis, S. K. (The lower portion of the lorica, to save 

 space, has been omitted, but is represented in its entirety at 

 %. 26.) X 2000 diameters. 

 Fig. 22. The same monad, having withdrawn its collar and flagellum, 



assuming an amoeboid state. 

 Figs. 23-25. Successive phases following upon the amceboid condition of 

 the same animalcule, corresponding with those illustrated by- 

 figs. 3-8 of the sponge-monad, and terminating in the production 

 of a similar morula-like aggregation of segment-masses or blas- 

 tomeres. 

 Fig. 26. The segment-masses or blastonieres of the preceding morula-hke 

 body becoming separated from one another, and issuing from the 

 parent lorica as simple flagellate monads or swarm- spores ; these 

 subsequently become attached, and grow to the adult state. 

 Fig. 27. An adult individual of Messrs. DoUinger and Drysdale's " hooked 

 monad" (Hctcromita uncuiata, S. K.). 



