372 M. F. E. Schulze on the Relationship 



reproductive cycle of the Sponges and Choanoflagellata, 

 asserted by Saville Kent, I must, in the first place, remark, 

 that since Lieberkiihn's discovery of the spermatozoa of 

 Spongilla, structures have been detected in numerous sponges 

 agreeing in their form, development, and kind of movement 

 so completely with the spermatozoa of the higher animals, 

 that no doubt can exist as to their true nature. Thus, even 

 if we should not place full confidence in the statements as to 

 the direct observation of the act of fertilization, there is the 

 less reason to doubt of the sexual reproduction of the Sponges, 

 as ova of typical structure, the development of which into 

 free larva? could in many cases be followed, have certainly 

 been detected almost everywhere. 



Saville Kent, it is true, disputes the occurrence of sperma- 

 tozoa in Sponges, as, indeed, he does not admit any true 

 sponge-ova ; nevertheless it appears from his own descriptions 

 and figures*" that he has himself seen sperm-balls and their 

 developmental stages. Only he has regarded them, together 

 with structures of quite a different kind (such as granules of 

 colouring-matter and cells containing reserve-nutriment), as 

 spore- aggregates and their formative stages. 



If, therefore, the Sponges possess a sexual reproduction, of 

 which the Choanoflagellata (as probably all the Protozoa) 

 are destitute, we find in this important difference a further 

 confirmation of the conviction arrived at from the anatomy 

 and histology of the two groups of animals, that the Sponges 

 are not colonies of Flagellata, nor, indeed, Protozoa at all, but 

 true Metazoa. 



Finally, the same result is furnished by the developmental 

 history. For different as may be the course of development 

 in the Sponges hitherto investigated, and greatly as the 

 accounts of individual observers may differ from each other, 

 all the statements nevertheless agree, that at the close of larval 

 life two different cell-lay ers^ an external and an internal one, 

 may he distinguished. In this there would be nothing to 

 alter, even if Gotte's statement (Zool. Anzeiger, nos. 183, 

 184) should prove to be correct, namely, that the ectoderm 

 of the larvse of Spongilla fluviatilis, which consists of flagel- 

 late cells, is entirely destroyed by exfoliation or atrophy. 



If, therefore, there is no doubt as to the Metazoan nature of 

 the Sponges, and consequently all justification of placing 

 them among the Choanoflagellata is entirely excluded, there 

 still remains the possibility that an affinity of the nature of a 

 relation of descendance may exist between these two groups of 

 animals whose degree of development is so different. 



* ' Manual of the Infusoria/ pi. x. 



