100 B. W. PRIEST ON THE CALCAREA. 



The number of species belonging to this group are few, com- 

 pared with the Keratosaand Silicea, but we keep gradually adding 

 fresh specimens year by year, for out of the thirty species dredged 

 by the Challenger, twenty-three were new to science, and within 

 the last twelve months Mr. Carter has described several new ones 

 from South Australia. 



The late Dr. Bowerbank enumerates only 12 species in his Mono- 

 graph on the British Sponges ; eight new forms may now be added 

 to these. 



The Calcarea are properly littoral, growing on or hanging from 

 rocks, seaweeds, corallines, &c, between tide marks, and often 

 being found in the pools left behind by the tide on our coasts. 



In 1828 the Bev. Dr. Flemming placed all the Calcarea then 

 known under one heading, viz., Grantia, in compliment to Dr. 

 Grant for the services he had done in working out the physiology 

 of the group. But as time went on it became necessary to alter 

 the classification by degrees, as fresh knowledge was acquired, 

 until it has reached the present stage. 



I will not trouble you by going over the various systems, but 

 state at once how the Calcarea stand as a group from the latest 

 investigations. I may find it still necessary, perhaps, to retain 

 familiar names, with regard to the description of species, as time 

 will not allow me to do more than describe one species in each 

 family, and that I shall have to condense into as small a space as 

 possible. 



The Calcarea, then, are now classed by the peculiarities of their 

 canal system, the early development of the mesoderm, the fact 

 of the mesoderm giving origin to the generative products, and, as 

 asserted by some naturalists, the absence of nervous elements, 

 although what a certain structure met with in the examination of 

 the sponges can be, but a nervous cell development in a rudimen- 

 tary state or otherwise, I cannot well see. 



According to Dr. Polejaeff, they form an isolated group within 

 the sub-type of an independent subdivision of the Ccelenterata, and 

 are divided into two Orders, Homocaila and Heterocwla y including 

 the Family Asconidw of Haeckel, only in the former, and the two 

 Families Syconidw and Leuconidce (Haickel), in the latter, with the 

 establishment of a third comparatively new Family, Teichonida, of 

 Carter. 



The Asconidai, from the Greek Ao-kov, a flask or leathern 



