298 Royal Society : — 



the squamiform and spinous appendages, more or less constant in 

 the macrourous Decapods, but lost in the short-tailed genera, and 

 the organ itself is gradually increased with cAery successive moult. 

 This is true, more or less perfectly, of all the other appendages pre- 

 sent in the larvae of all Decapoda ; and no change of form, as under- 

 stood in the term metamorphosis as applied to insects, takes place in 

 the development of Carcinus. That the distance between the old 

 and young forms is the result of an exaggeration of parts in the 

 larva as compared with the relative proportion of the same in adult 

 animals, together with the absence of others, which are gradually 

 produced, and assume the permanent condition of the adult type. 



The author has observed the rudiments of the future legs shortly 

 after birth. Ke has dissected and figured eight or nine of the more 

 important stages, and shown the relative alteration of each part con- 

 secutively, commencing with the Zo'ta taken from the egg, and pur- 

 sued the observations through the older forms to that of the adult 

 Carcinus. 



"On the Anatomy and Physiology of the SpongiadeB." By J. S. 

 Bowerbank, F.R.S., F.L.S. &c. 



The arrangement of the Spongiadce by Lamarck, based entirely ou 

 external form, is wholly inadequate for the discrimination of species. 

 The classification adopted by Drs. Fleming, Grant, and Johnston, 

 dependent more especially on the chemical constituents of those 

 bodies, is far too limited to be applied in generic characters. The 

 author has, therefore, for this purpose rejected both systems, and has 

 retained the latter one for forming primary divisions only ; he 

 purposes founding the generic characters principally on the organic 

 structure and mode of arrangement of the skeleton, in accordance 

 with the practice so generally adopted by naturalists with regard to 

 many of the higher classes of animals. Tethea, Geodia, Dysidea and 

 a few others are the only well-defined genera that have yet been 

 established ; while others, such as Halichondria, even in the narrow 

 circle of the list of British species, contain at least ten distinct 

 modes of arrangement of the skeleton, each of wliich is constant and 

 well-defined in its character. 



It is not intended to propose the rejection of any of the well-esta- 

 blished genera of preceding authorities, but to confine each genus 

 strictly within the bounds indicated by the peculiar mode of struc- 

 ture of the skeleton which exists in that species of sponge which is 

 the oldest- established and best-known type of the genus, and to refer 

 all others that may distinctly differ from that type to new genera 

 founded on structural principles. 



It is proposed to characterize the elementary tissues in the follow- 

 ing order : — 



1. Spicula. 



2. Keratode or horny substance. 



3. Membranous tissues. 



4. Fibrous tissues. 



5. Cellular tissues. 



6. Sarcode. 



