180 METAMORPHOSES OF MAN 



endeavour to separate the general and best-ascertained 

 results, from the chaos of numberless contradictions 

 presented by the writings of those most distinguished 

 in this branch of study.* 



The sponges are truly compound animals, although it 

 would be very difficult if not impossible to distinguish 

 a single individual. These beings, whose position is 

 still regarded by some naturalists as problematical, 

 possess a framework which is either horny or cal- 

 careous, and is frequently represented by a network 

 of simple spines or spicules. There is spread over 

 this form of skeleton, a sort of organized varnish or 

 coating, which extends to the very smallest rami- 

 fications. This varnish is really the living matter which 

 constitutes the animal ; and each species, although 

 having the elements common to all, is as variable in 

 form and proportions as a polyp colony. 



Like the latter, the sponges can be reproduced 

 both by gemmation and fissuration. Grant's f obser- 



* Notwithstanding the many .improvements which the micro- 

 scope has undergone for the last thirty years, it is still far from 

 supplying the wants of Histologists. In order to become accurately 

 acquainted with many details, it would be necessary to have a 

 magnifying power of from ten to twelve hundred diameters, with 

 the same clearness and definition as one of three or four hundred 

 diameters. My opinions on this matter are as decided as they were 

 twenty years ago, when I was engaged in the study of this group. 

 Of all my researches on this subject, I only published a short note 

 which was addressed as a letter to M. Dujardin, and which he 

 inserted in his article on Infusoria in D'Orbigny's dictionary (1846), 

 although it was in opposition to his fundamental views. This note 

 seems to have been unnoticed by most naturalists who have since 

 written upon this subject, among others by MM. Claparede and 

 Lachmann. 



t Grant's writings date from 1826, and appeared in the "Edin- 

 burgh New Philosophical Journal." 



