Miscellaneous. 307 



sequence proposed already, in my monograph of the Monera, and, 

 later still, in my 'Natiirliche Schopfungsgeschichte,' to unite these 

 three last-named classes under the ancient name of Acalephes or 

 Cnidae (urticant animals)." 



Notwithstanding the existence of this differential character, the 

 idea that the sponges are only an inferior group of the Ccelenterata 

 had gained ground. Thus M. Glaus, in the second edition of his 

 work on zoology, divides the subkingdom of the Ccelenterata into 

 three classes — namely, the Spougiic, Anthozoa, and Ctenophorae. This 

 grouping, which might appear rather rash, has just been confirmed in 

 a striking manner by the discovery, due to M. Eimer, of urticant 

 organs in the sponges. This naturalist has observed some organs of 

 this nature in a certain number of siliceous sponges more or less re- 

 lated to the ReniercB. 



In one species with remarkably viscoiis sarcode the urticant cells 

 are found disseminated without aiiy regular arrangement, but never- 

 theless frequently round the spicules, and most frequently surrounding 

 throughout their whole extent the openings which give access to the 

 afferent currents. They cover in particular abundance the cavity 

 of the stomach ; it seems, on the contrary, that they are wanting 

 at the surface of the animal. Their form is an abbreviated oval, as 

 in many of the Ccelenterata. Amongst those which are completely 

 developed, niimerous cells in the course of formation are found. 



The second species which has presented urticant cells has oscula 

 opening most frequently on papilliform eminences and conducting 

 into canals lined with an extremely distinct membrane. It is this 

 membrane which is furnished with urticant cells, in all degrees of 

 development ; they are more spherical and a little smaller than in 

 the preceding species. Where the canals abut on the exterior sur- 

 face of the body, they give place to ordinary cells. 



A third species of sponges with urticant cells approaches very closely 

 to the preceding, but differs from it by the absence of a cutaneous 

 layer and in the nature of its spicules. The canals serving for the 

 passage of the efferent currents are of the same width, and have the 

 same arrangement as in the preceding, except that they are only 

 lined with a very delicate membrane — so delicate, in fact, that it is 

 often difficult even to prove its existence. This membrane bears the 

 urticant cells and cells of formation in all degrees of development ; 

 but the urticant cells are very rare in the midst of the others. This 

 species, which thus forms a passage between the sponges with urti- 

 cant cells and those which are destitute of these organs, may be re- 

 garded as an arrest of development of the preceding. 



The fourth form has no trace of a membrane lining the tubes 

 which serve for the passage of the efferent currents. Its tissue, in 

 most cases, is still more delicate than that of the preceding, from 

 which it differs also in the spicules. It is ordinarily colourless ; but 

 yet individual specimens are found which have a slight reddish-blue 

 colour ; and from these we pass to others which are of a violet-blue. 

 Among a great number of specimens of the bluish variety, M. Eimer 

 has found some which were filled with urticant cells of a type totally 



