66 OPINIONS AND DISCOVERIES 



tui'e imperfectly, and presenting the first appearance of that 

 nature in the presence of (unlined) excavations in their 

 interior for digestive purposes. They are passive, acritous 

 and unique, — that is to say, not divisible into groups of 

 the same value with the groups to which any of the other 

 typical di^^sions of the animal kingdom can be divided* 



There must be sometliing in the structure of the sponge 

 to give rise to these ingenious views, which are undoubt- 

 edly at variance with the usual definition of an animal ;t 

 and appear indeed to have been formed to obviate the 

 objections that have hence been made to the admission of 

 the sponges into that kingdom. What is there outwardly 

 more universally characteristic of animality than a defined 

 and limited figure repeating itself, with minute exactness, 

 tlu'ough successive generations ? But the amorphous de- 

 velopement of sponges is so remarkable that it has given 

 the family a name (Amorphozoa), and finds no parallels 

 excepting among the lowest tribes of vegetables. And than - 

 irritability there is no other inherent quality of a structure 

 tiiat affords unequivocal evidence of the existence of ani- 

 mal life in it ; and yet here there is no symptom of such a 

 quality. 



But it is affirmed that the numerous analogies of structure 

 and composition which may be traced between sponges and 

 other well knowm genera of zoophytes prove their mutual af- 

 finity, and the relationship to be indeed so close that the sepa- 

 ration of them into distinct orders can be of no advantage to 



* 1 am reminded by this view of the sponge, of Linnaeus' definition of 

 a vegetable: — " Vegetabile est vita composita, absque motu vohnitario." 

 yyst. Reg. Veg. p. 3, 



t Sponges do not possess one of the nine essential characters of ani- 

 mal life given by Lanwvck. Anim, s. Vert. i. p. 96. •2de edit. 



