434 



CHAPTER IX. 



MICROSCOPIC FORMS OF ANIMAL LIFE : — PROTOZOA; 

 ANIMALCULES. 



324. Passing-on, now, to the Animal Kingdom, we begin by- 

 directing our attention to those minute and simple forms which 

 correspond, in the Animal Series, with the Protophyta in the 

 Vegetable (Chap, vi.) ; and this is the more desirable, since the 

 formation of a distinct group to which the name of Protozoa (first 

 proposed by Siebold) may be appropriately given, is not merely 

 one of the most interesting results of recent Microscopic inquiry, 

 but is a subject on which it is particularly important that the 

 Microscopic observer should know what the Physiologist believes 

 himself to have ascertained. This group, which must be placed at 

 the very base of the Animal scale, beneath the great Sub-Kingdoms 

 marked-out by Cuvier, is characterized by the extreme simplicity 

 that prevails in the structure of the beings composing it ; for in 

 the lowest of them there is absolutely nothing that can be properly 

 called 'organization,' while in the highest there is no such dif- 

 ferentiation of parts as constitutes the ' organs ' of even the 

 simplest Zoophyte or Worm. — As we have seen (§ 183) that 

 among the lowest Protophytes all the essential processes of Vege- 

 tative life may be carried on by a minute mass of ' protoplasm ' 

 which is not even bounded by a distinct limitary membrane, so 

 as to constitute a cell, — the differentiation between cell- wall and 

 cell-contents not having yet manifested itself, — so amongst the 

 lowest Protozoa we find the power of maintaining an independent 

 existence of a kind essentially similar to that of the higher Ani- 

 mals to be possessed by similar particles of that peculiar blastema, 

 or formative substance, to which the name sarcode (expressive of 

 its rudimental relation to the flesh of higher animals) was given 

 by Dujardin, who first drew attention to its extraordinary endow- 

 ments. This Animal ' sarcode ' very closely resembles the ' proto- 

 plasm' of Vegetables in chemical composition and behaviour with 

 re-agents, and in many of its vital manifestations ; but a definite 

 distinction seems to exist between even the simplest Protophyte 



