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



to the remarkable form recently described by Prof. Haeckel 

 under the title of MagosphcBra planuluj represented by PI. VII. 

 figs. 13 to 18, and whose developmental phases correspond re- 

 markably with those of the so-called ciliated sponge-embryo as 

 just described. Placing our data in the same order of succes- 

 sion, we find first the reptant amoeboid body, which assumes a 

 rounded quiescent state, and then divides by a similar process 

 of segmentation into a morula or spherical aggregation of 

 rounded corpuscles. These separated segments or blastomeres 

 now spread out on the surface, imparting to it a prismatic or 

 tessellated aspect, as in the sponge-embryo, and further taper 

 backwards and are united to one another posteriorly in a cor- 

 responding manner. We have now, indeed, only to add 

 a hyaline collar and single cilium or flagellum to the peripheral 

 border of each unit in place of the several cilia which clothe 

 this region in Magosphcera, to produce a morphologically iden- 

 tical organism. What now becomes of Magosphcera ? After 

 swimming for a considerable while in the open sea, it breaks up 

 or resolves itself into its constituent elements, each separated 

 conical unit shortly afterwards losingor withdrawing its ciliary 

 appendages and assuming an amoeboid phase, identical with that 

 from which the spherical colony-form first sprang, and prepared 

 once more to repeat the cycle. A closely similar developmental 

 cycle has recently been shown by Messrs. Dollinger and Drys- 

 dale to take place among many of the simple Monadina — an 

 encysted spherical zooid splitting up by longitudinal and trans- 

 verse cleavage into a morula-like aggregation, each segment 

 of which develops into a distinct individual. My own recent 

 investigations associated with this humble organic group have 

 so abundantly confirmed the results of those of the authorities 

 just quoted that I am inclined to regard this developmental 

 cycle, in conjunction with another, referred to later on, as 

 common to the greater portion of the representatives of the 

 Infusoria Flagellata. The successive phases from the free- 

 swimming monad to the moruloid stage of one of the most 

 prominent types described and figured by the gentlemen last 

 mentioned, in the 'Monthly Microscopical Journal' for January 

 1874, is reproduced at PI. VI. figs. 27 to 33, and may be 

 instructively compared with the similar cycle as it occurs in 

 Magosphcera and the sponge-gemmules illustrated in the same 

 and accompanying plates. Folytoma uvella, which is likewise 

 figured and described by Messrs. Dollinger and Drysdale under 

 the name of the "biflagellate or acorn monad," exhibits the 

 same multiple fission or moruloid mode of reproduction — a fact 

 amply attested even by such early investigators as Ehren- 

 berg, Perty, and Schneider. A remarkable feature presented 



