1900] MICROSCOPICAL JOURNAL. 341 



the Lelapia, as a living representative of the same group. 



Further details as regards the anatomy of many of the 

 local forms of calcareous sponges can be obtained from 

 the articles by Professor Dendy published in the Proceed- 

 ings and Transactions of the Royal Society of Victoria 

 and the Quarterly Journal of Microscopical Science. 



We commenced with the question, Are sponges ani- 

 mals or plants ? and our examination of the circulatory 

 and digestive system indicates their animal status. But 

 the most convincing evidence, placing them, without 

 doubt, amongst the animals, comes from a study of their 

 development. In this they are distinctly holozoic. That 

 we may learn a few facts about the general principles of 

 sponge development it will be well to take as a type Sy- 

 con raphanus, because it is easily obtained, and, in the 

 summer season, is usually well provided with embryos in 

 every stage of development. These stages may be noted : 



(1). Reproductive cells are formed from cells in the 

 mesoderm of the sponge and the productive elements — 

 male and female — are fashioned from them. The male ele- 

 ments or spermatozoa are formed by the division of these 

 reproductive cells into a large number of parts each of 

 which develops a head and tail, whilst the female cellsor 

 ova become somewhat spherical in shape and are furnish- 

 ed with a large nucleus. 



(2). The ova of one sponge are probably fertilized by 

 the spermatozoa from another and then commence to de- 

 velop in the mesoderm of 'the mother sponge near the 

 walls of the flagellate chambers. 



(3). Each ovum begins to divide in an orderly manner 

 into 2, 4, and 8 parts, and so on — the cells at the upper 

 pole being somewhat columnar in shape whilst those at 

 the lower pole are spherical and granular. (A. 1, 2, 3, 4.) 



(4). A little later and these layers are clearly marked 

 off from each other with a cavity between them and the 

 blastosphere stage is reached. (A. 5.) 



