100 Dr. P. H. Carpenter on some Points in 



sponge under all circnrastances. How long these canals may 

 be, whether they perforate the thin wall of an Olynthus as 

 simple apertures, or in other forms traverse the thick body- 

 wall as a system of profusely branched and frequently anasto- 

 mosing passages, is quite irrelevant, and depends solely upon 

 the degree of development of the mesoderm. It might per- 

 haps still be objected that the canal-system of the Sponges is 

 developed in such different ways that it certainly cannot always 

 take its origin from the primitive gastral cavity, but at least 

 as often be formed by gaps which make their appearance 

 in the mesoderm, and growing on centripetally and centrifu- 

 gally, perforate the gastral and dermal surfaces of the sponge- 

 wall only in the second line. But we must not overlook one 

 thing : how is the gastrula of the sponge formed ? In per- 

 fectly analogous ways : some by invagination, and with this 

 process the formation of the gastral canals from the stomach 

 outwards may be compared ; the others by the appearance 

 first of all of a cavity in the ccsnoblasteraa and its subsequent 

 breaking through outwards ; and this may be placed side by 

 side with the origination of the canal-system from gaps occur- 

 ing in the mesoderm. I believe that the former process, as 

 well as the formation of the gastrula by invagination, is the 

 older and more typical, and that the second must be accounted 

 for by some phenomena of adaptation sui generis. 



In conclusion, I must again assert that it seems to me, so 

 far as the conditions are at present before us, that the argu- 

 ments which have been urged against the Ccelenterate nature 

 of the Sponges are far from counterbalancing those which are 

 in favour of it. 



XII. — On some Points in the Morphology of the EchinoderniSj 

 and more especially of the Crinoids. By P. Herbeet Car- 

 penter, D.Sc, F.R.S., Assistant Master at Eton College. 



In a recent number of the 'Revue Scientifique '"^j Professor 

 Edmond Perrier has published a short and semipopular 

 article, the title of which appears in the table of contents as 

 " Les Encrines Yivantes, d'apr^s les Explorations du Chal- 

 lenger.''^ The author's treatment of his subject, however, is 

 not altogether in accordance with the expectations to which 

 such a title gives rise ; for his article is headed simply " Les 

 encrines vivantes," and of the six columns to which it 



* Revue Scientifique, tome 35. No. 22, 30 Mai, 1885, pp. 690-693. 



