METAZOA PORIFERA. 63 



fore it is plain, says Ryder, that if these organs are visual 

 or sensitive to light or any other natural agent, they are 

 best developed in just the position in which they are of 

 the most service to the organism. 



METAZOA. 



PORIFERA. 



Section i (erect part). 



Great advances have been made in the direction of a 

 natural classification of the Porifera since 1872, but 

 nevertheless naturalists still differ not only in regard to 

 the systematic position of these animals, but also in 

 respect to their anatomical structure. 1 



They are considered as members of the next more spe- 

 cialized subkingdom, the Coelentera, by Haeckel, Leuck- 

 art, Marshall, Polejaeff, Schulze, R. von Lendenfeld, 2 

 and Ganin. Marshall 3 even goes so far as to regard them 

 as reduced members of this group, finding evidences, as 

 he thinks, of the former existence of tentacles, thread 



1 Dr. R. von Lendenfeld has given a clear and an extremely inter- 

 esting history of our knowledge of sponges in the Introduction to 

 his Monograph of the Australian Sponges, Proc. Linn. Soc. New 

 South Wales, IX, part i, 1884. For the most complete bibliogra- 

 phy on the subject, see RaufFs great work on Palaeospongiologie, 

 Palaeontographica, XL, i893~'94. 



2 According to this author the Metazoa are naturally divided into 

 two groups or grades ; the Coelentera with a simple undivided body 

 cavity, all the parts of which are in direct connection with one 

 another ; and the Coelomata, which have two distinct and entirely 

 separated body cavities, a gastral and a perigastric cavity. The 

 sponges, according to this author, have a simple and continuous 

 body cavity, so that they are regarded by him as Coelentera (Proc. 

 Zool. Soc. London, 1886, p. 565). 



3 Zeitschr. f. wiss. Zool., XXXVII, 1882, p. 246. Jena. Zeitschr., 

 XVIII, 1885. See Ann. and Mag. Nat. Hist., (5), XVI, 1885. 



