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



the independent collar-bearing types, such as Saljnngoeca, and 

 the majority of the Infusoria flagellata. That these bodies 

 cannot in any way be compared with the true ova of the ordi- 

 nary Metazoa is demonstrated not only by their inconstant 

 form and character, disassociated also with any act of spermatic 

 fecundation, but from the fact that the segmentation of the 

 primary unit gives rise to a morula-like aggregation, Avhich 

 does not develop by the fusion of its constituent particles ox 

 blastomeres into a single germ-lamella or blastoderm, but 

 into a number of distinct and independent unicellular zooids 

 or units. The Metazoic interpretation of the nature of sponges, 

 as grounded upon the developmental manifestations of these 

 same bodies, must likewise as a consequence be abandoned, or 

 otherwise be extended to the simple Monadina, Radiolaria, 

 and Catallacta, which produce a similar morula-like segmen- 

 tation-mass, thus leaving the Protozoa in possession only 

 of little more than an empty title. The true nature and sig- 

 nificance of the so-called ciliated embryos of the sponge, while 

 not reconcilable with the proposed Metazoic interpretation, 

 becomes clearly intelligible on collating these organisms with 

 the unicellular Protozoa. Regarded from this position, the 

 identity of the ovate aggregation of separate units which con- 

 stitute the so-called sponge-embryo with the similar aggrega- 

 tion of units of the segmented monad, afterwards separated and 

 dispersed as swarm-spores, is made apparent. This sponge- 

 embryo is in this manner demonstrated to be merely an aggre- 

 gation of swarm-spores held closely bound to one another 

 throughout the process of development. It may therefore be 

 appropriately denominated a " swarm-gemmule," whose 

 mission it is in its aggregate condition to lay the foundation 

 of a composite sponge-stock similar to the one which gave it 

 birth, and in a manner identical with that individually effected 

 by each motile swarm-spore of the solitary monad. 



As a final demonstration of the Protozoic nature of sponges, 

 the multiplication of these organisms by the production of 

 countless infinitesimal spores after the manner of the typical 

 Monadina has been determined. This spore-formation is 

 brought about through the assumption by the matured collar- 

 bearing zooids of a quiescent encysted state, accompanied or 

 not by the fusion of two individuals. The spores produced by 

 the breaking up into almost invisibly minute particles of tlie 

 entire protoplasmic substance of the encysted zooids are libe- 

 rated in the substance of the syncytium ; and within this 

 matrix each spore develops again through an amoeboid or 

 cytoblastic and then simply flagellate phase to an adult collar- 

 bearing unit. This multiplication of the typical sponge- 



