214 Mr. W. S. Kent on the Eelationshijj of 



Hackel's "ontogenetic" arguments in favour of the close 

 relationship of the sponges to the corals next attract our atten- 

 tion ; but whatever " phylogenetic " significance may be at- 

 tached to them, it is quite sufficient to reply that evidence of 

 affinity may be substantiated on equally strong grounds be- 

 tween the respective classes of the Scolecida, the Annelida, 

 and theEchinodermata, these all originating, in common with 

 the sponges and corals, (from free-swimming ciliated larvje in 

 possession of a simple digestive cavity, opening outwards by 

 a single terminal orifice. 



We are now in a position to demonstrate not only that the 

 representatives of the Porifera, or sponge-class, are quite dis- 

 tinct from the Actinaria or Coelenterate coral-forming animals, 

 but that they belong to a section peculiar in itself, and far less 

 highly organized. 



Commencing with the alimentary apparatus. It has been 

 shown that the buccal orifice in the Coelenterata is single and 

 terminal. In the Spongiadaj, on the contrary, its homologue 

 consists of a multitudinous and indefinite number of apertures 

 which perforate the body-wall of the organism. 



In the Coelenterata this single buccal orifice is also the 

 channel through which all excretory matters are voided. In 

 the Spongiad^ there are distinct apertures, the flues or oscula, 

 set apart for the purpose of carrying off the effete matters. 



All Actinaria are provided with tentacles, or, where these 

 are rudimentary, with a prehensile and protrusible buccal ori- 

 fice, wherewith they sieze and secure their prey. The most 

 highly developed sponges are dependent on the action of ciliary 

 currents for the acquisition of the nutrient matters which sup- 

 port them. 



This last diagnosis may, I think, be regarded as one of the 

 highest importance, — the one force (in the case of the Actinaria) 

 being exerted by the free will of the animal, and the other 

 one, we have every reason to believe, being purely involun- 

 tary and vegetative. Dr. Bowerbank himself directs atten- 

 tion to the fact that the ciliary action which progresses within 

 the interstitial cavities of the sponge is precisely similar in 

 its nature to what obtains in the ciliated epithelium of the 

 higher vertebrata ; this Ave know to be involuntary : have we 

 any reason for sujiposing that it assumes a more complex 

 nature in the low-organized animals now under consideration ? 

 One objection that will probably be urged, as inconsistent with 

 the theory of the sponges acquiring their nutriment through 

 the agency of involuntary action, is the fact that at different 

 periods the inflow of water through the j)ores varies much in 

 the strength of its action. This objection, however, is easily 



