THE SPONGIDA OR PORIFERA. 357 



through the oscula of the sponge into the surrounding water. 

 "In their most characteristic form," writes Saville Kent, "these 

 reproductive bodies, or cell-aggregates, consist of a uniform series 

 of collared zooids ; but by irregular growth one-half may arrive at 

 or pass maturity in advance of the other, the product then being 

 a compound structure, presenting a close correspondence with that 

 phase of development of the Metazootic ovum known as the 

 amphiblastula. Since, however, these bodies are in no way com- 

 parable with the Metazootic ovum — not being the product of the 

 concourse of true sexual elements — the above likeness is simply 

 homoplastic, and the body as a whole, consisting as it does of an 

 aggregation of numerous independent zooids, may be most appro- 

 priately denominated a ' swarm-gem mule.' " 



For want of space, we cannot dwell further on this interesting 

 subject ; but the few remarks offered by us suffice to show the 

 sharp divergence of opinion that exists among biologists as to the 

 real position of the Sponges. The views advanced by Haeckel in 

 the first instance, that the sponge-body can be shown to consist of 

 an ectoderm, mesoderm, and endoderm, that spermatozoids are 

 present in the Spongida, and that the reproduction of this interest- 

 ing group of animals takes place by means of the development 

 and segmentation of true ova or eggs, are all stoutly and diamet- 

 rically opposed by Saville Kent and those who think with him. 

 The latter authority argues his case, we think, with great force and 

 consummate ability in the article " On the Nature and Affinities 

 of the Sponges," and in other parts of his "Manual of the Infu- 

 soria " ; and supports his views with beautiful drawings illustrative 

 of his own personally conducted investigations. 



The questions at issue require for their solution a careful, 

 minute, and laborious investigation of the vital microscopic 

 elements of sponge structure, and especially of the origin, life- 

 history, and development of the reproductive bodies of this group 

 of animals. To those who have leisure, and a leaning towards 

 biological pursuits, here is a fine field open for the display of 

 industry and skill in delicate scientific research. 



