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



modification of Prof. Haeckel's original interpretation of the 

 so-called ciliated larvaj or reproductive gemmules of sponges, 

 we can by no means be said to be in possession of an exhaus- 

 tive knowledge of the histiological or developmental manifes- 

 tations of these remarkable bodies. Our apprehension of the 

 morphological affinities of the sponges as a class, again, 

 assisted only by the dim and deceptive light derived from this 

 same imperfect knowledge of these reproductive gemmules, is, as 

 a natural consequence, encompassed by a still more perplexing- 

 mist of doubt and obscurity. Animated with the desire of 

 contributing, however slightly, towards a more full and accu- 

 rate comprehension of the true nature and affinities of that 

 organic group with which these debatable structures are 

 associated, I propose here to place briefly on record the 

 results of an extended personal investigation of these special 

 sponge-elements, paying attention more particularly to those 

 phenomena observed which appear so far to have escaped the 

 observation of the authorities just named. 



As a preliminary introduction, it is scarcely necessary to re- 

 mark that this embryological question is here approached from 

 a direction diametrically opposite to that selected, with but 

 one, if any, exception, by all of the before-mentioned investi- 

 gators. These latter, although differing slightly among them- 

 selves in their individual interpretation of the structural 

 elements of the so-called sponge-embryos, agree- with one 

 another, and, so far with Haeckel, in according to these bodies, 

 and, pari passu, also to the adult sponges, the existence of two 

 or more distinct cellular layers. This concession necessarily, 

 and by these authorities avowedly, carries with it the inference 

 that sponges are true tissue-forming Metazoa, and, at any 

 rate, more nearly related to the simplest tissue-forming Coelen- 

 terata than to the Infusoria or other typical Protozoa. Mr. 

 Carter even commits himself so far, though perhaps not 

 intentionally, to this metazoic interpretation as to continually 

 make use of the terms " ectoderm " and " ectodermal layer " 

 in his account of sponge-development. In accordance with the 

 views adopted by myself, which are identical with those held by 

 the late Prof. H. James-Clark, and as explained by me at some 

 length in last January number of this Magazine, the sponges 

 are compound colony-building collar-bearing flagellate monads, 

 exhibiting neither in their embryological nor in their adult 

 condition phenomena that do not find their parallel among the 

 simple unicellular Protozoa, from which group, as a neces- 

 sary consequence, this identity being established, they cannot 

 consistently be held separate. The so-called " ciliated 

 embryos " or " larvse " of the various sponge-forms, following 



