EXPLANATION OF PLATE IX. (continued). 



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 of the opposite extremity as to have withdrawn their collars and flagella, 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) CILIATUM, Bwbk. Variety of "amphiblastuloid" type of 

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

 metamorphosed spongozoa presents an intermediate condition of development 

 as compared with the series above and below it. 



31,32. GRANTIA COMPRESSA. Irregularly developed " amphiblastuloid " swarm gem- 

 mules. 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 33 and 34, " Amphiblastuloid " swarm-gemniules, 

 as represented by F. E. Schulze ; in the first of these the amoeboid units are 

 invaginated within the uniflagellate, or so-called ectodermal 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. 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 at a a 

 cell-spherules derived by metamorphosis from the constituent uniflagellate 

 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 preceding figure; 39, one such cell-spherule 

 further enlarged, subdivided by segmentation into spore-like elements (Oscar 

 Schmidt). 



40,41. HALISARCA LOBULARIS, Duj. 40, Optical transverse section of "planuloid" 

 swarm-gemmule, showing enclosed closely corresponding and similarly 

 derived cell-spherules, which are identified by Metschnikoff with the primi- 

 tive condition of the rosette-gemmules represented at Figs. 15-17 ; 41, one 

 such cell-spherule further enlarged (Metschnikoff). 



