Mr, W. S. Kent on the Embryology of Sponges. 145 



by the type last named is, that the flagella remain intact and 

 the animalcule swims actively about while the segmentation 

 of its entire interior substance is progressing. 



One specially important factor associated with the develop- 

 mental cycle of the ciliated sponge-gemmule,that has so far been 

 quite lost sight of, relates to the initial condition of the so-called 

 Amosha-like ovum, which by its segmentation develops into the 

 compound structure. How is this presumed ovum produced ? 

 Haeckel and his followers regard it as the independent pro- 

 duction of an imaginary entodermal tissue. I concede to it the 

 position merely of metamorphosed collar-bearing sponge-monad, 

 which having arrived at mature age has assumed an amoeboid 

 phase in a manner precisely identical with that which obtains 

 in Magosphcera and among many of the simpler free-swimming 

 monad forms just referred to. Such an assumption by the collar- 

 bearing monads or spongozoa of an amoeboid state has been 

 personally witnessed over and over again, and is, moreover, 

 amply confirmed, though not with the interpretation here 

 submitted, by Haeckel, Carter, and all other authorities who 

 have concentrated their attention on this organic group. The 

 dimensions furthermore given by Mr. Carter of the smallest 

 ovum -like body observed by him correspond precisely with 

 those of a single collar-bearing spongozoon. As a final link 

 in the chain of evidence it remains to be shown that a parallel 

 mode of reproduction is associated with those independent 

 collar-bearing monads that formed the subject of my last year's 

 communication to the Linnean Society. A single example 

 out of innumerable instances that might be quoted will suffice 

 to demonstrate this fact. The solitary loricated type Salpin- 

 goeca fusiformis, nobis*, represented at PI. VI. figs. 21-26, 

 exhibits precisely similar phenomena. Commencing first with 

 the typical collar-bearing phase, it next assumes an amoeboid 

 condition, then, contracting into a subspherical quiescent state, 

 splits up by symmetrical longitudinal and transverse cleavage 

 into a spheroidal mass of minute segments or blastomeres cor- 

 responding essentially with that produced in a parallel manner 

 by the so-called sponge-embryo. The further development 

 of the ultimate segments or blastomeres is likewise identical. 

 The most conspicuous primary transformation of the segmental 

 units consists in both instances of the acquirement of a single 

 flagellate appendage ; and this is next succeeded by the growth 

 of the characteristic collar. The only distinction subsisting 

 between the two is, that while the individual units in the case 



* Since figured and described by O. Butscbli in Siebold anil KoUiker's 

 'Zeitschrift fiir wissenschaftliche Zoologie ' for January 1878, under the 

 title of Salpingaecn Ckirkii. 



Ann. & Mag. N. Hist. Ser. 5. Vol. ii. 10 



