144 Marvels of Pond-Life. 



called thread-cells or nematocysts/^ In describing the 

 Polyps we have given illustrations of these weapons. 



The remaining classes^ which have been roughly 

 associated as Protozoa, must evidently be rearranged. 

 Sponges^ Rhizopods (Amoebse, &c.), and Gregarines^ 

 have strong resemblances, but recent researches 

 may place the former higher. The Infusoria compre- 

 hend creatures too various to remain under one head, 

 and very many of them too highly organized to be 

 called ^^protozoons/' or first life-forms. 



Those who wish to pursue this subject further may 

 consult Professor Huxley^s ' Elements of Comparative 

 Anatomy/ from which the preceding quotations have 

 been taken. 



A system of classification founded upon anatomical 

 and developmental considerations frequently differ con- 

 siderably from one we might arrive at if all the crea- 

 tures were arranged according to the perfection of their 

 faculties and the extent and accuracy of their relations 

 to the external world. Such a classification would not 

 in any way supersede the former, but it would prove 

 very instructive and offer many valuable suggestions. 

 Some years since, Professor Owen proposed to divide the 

 Vertebrates according to the perfection of their brains, 

 but other anatomists did not find his divisions sufii- 

 ciently coincident with facts. Very little has been done 

 towards an exact science of human phrenology. The 

 difficulties remain pretty much as they were many years 

 ago, and our comparative phrenology, if we may use such 

 a term, is in a very imperfect state. When we come to 

 the lower animals we do not know what peculiarities 



