EXPLANATION OF PLATE IX. (cotttijt7ted). 



Fig. 



22-29 the base of the projecting flagellum ; through the enlargement and expansion 

 (continued), outwards of these constituent units the common body now possesses a dis- 

 tinctly developed central cavity; 25, more matured developmental phase of the 

 same planuloid type of gemmule, in which the common body is shown to be 

 composed of a symmetrically ovate aggregation of typical collared monads or 

 spongozoa, x 600 ; 26-29, diverse varieties and phases of development of the 

 " amphiblastuloid " type of swarm-gemmule from the same sponge, produced 

 through the uneven growth of the constituent collared monads or spongozoa in 

 the neighbouring halves of the common body ; in 27, 28, and 29, the collared 

 monads of the posterior region have developed so much in advance of those 

 of the opposite extremity as to have withdrawn their collars and flagella, 

 assumed an amoeboid condition, and coalesced more or less completely with 

 one another, x 600. 



30. Grantia (Sycon) CILIATA, Bwbk., vol, i. p. 178. — Variety of "amphiblastuloid" 

 type of swarm-gemmule, as represented by Barrois, in which an equatorial ring 

 of metamorphosed spongozoa presents an intermediate condition of develop- 

 ment as compared with the series above and below it. 



31, 32. Grantia compressa, vol. i. p. 178. — Irregularly developed "amphiblastuloid" 

 swarm-gemmules. At 31 (after O. Schmidt) the more matured amoeboid 

 units have become invaginated within the primitive central cavity of the 

 common body. 



33-35. Sycandra raphanus, Hkl., vol. i. p. 180. — 33 and 34, "Amphiblastuloid" 

 swarm-gemmules, as represented by F. E. Schulze ; in the first of these the 

 amoeboid units are invaginated within the uniflagellate, or so-called ecto- 

 dermal elements, while in the second one an entire opposite process, or the 

 invagination of the so-called ectodermal elements, is in course of progress ; 

 35, irregularly developed amphiblastuloid swarm-gemmule (after O. Schmidt). 



36-39. ASCETTA PRIMORDIALIS, Hkl., vol. i. p. 181. — 36, " Planuloid " swarm-gemmule 

 as seen in optical section, with internally contained cell-spherules ; 37 and 

 38, portions of lateral wall of a swarm-gemmule of the same sponge, showing 

 zX aa cell-spherules derived by metamorphosis from the constituent uni- 

 flagellate elements ; these assuming an amoeboid condition and apparently 

 coalescing with one or more neighbouring units, creep into and occupy the 

 common central cavity, as shown in the pi-eceding figure ; 39, one such cell- 

 spherule further enlarged, subdivided by segmentation into spore-like elements 

 (Oscar Schmidt). 



40,41. Halisarca lobularis, Duj., vol. i. p. 189. — 40, Optical transverse section 

 of " planuloid " swarm-gemmule, showing enclosed closely corresponding 

 and similarly derived cell-spherules, which are identified by Metschnikoff 

 with the primitive condition of the rosette-gemmules represented at Figs. 

 15-17 ; 41, one such cell-spherule further enlarged (Metschnikoff). 



