10 INTRODUCTION TO CLASSIFICATION. 



present, we know nothing whatever of this condition among the 

 Gregarinse ; so that in reasoning about them we must always 

 exercise a certain reticence, not knowing how far we may have 

 to modify our opinions by the discovery of the sexual state 

 hereafter. 



The process of becoming encysted, preceded or accompanied 

 very often by the mutual apposition of two Gregarinse, was for- 

 merly imagined to correspond with what is termed among plants 

 "conjugation," a process which in some cases, at any rate, 

 appears to be of a sexual nature. But the discovery that a 

 single Oregarina may become encysted and break up into 

 Pseudo-navicellse, seems to negative this analogy. 



II. THE EHIZOPODA. 



It seems difficult to imagine a stage of organization lower 

 than that of Gregarinida, and yet many of the Rhizopoda are 

 still simpler (Fig. 2). Nor is there any group of the animal 

 kingdom which more admirably illustrates, a very well-founded 

 doctrine, and one which was often advocated by John Hunter, 

 that life is the cause and not the consequence of organization ; 

 for, in these lowest forms of animal life, there is absolutely 

 nothing worthy of the name of organization to be discovered by 

 the microscopist, though assisted by the beautiful instruments 

 that are now constructed. In the substance of many of these 

 creatures, nothing is to be discerned but a mass of jelly, which 

 might be represented by a little particle of thin glue. Not that 

 it corresponds with the latter in composition, but it has that 

 texture and sort of aspect ; it is structureless and organless, and 

 without definitely-formed parts. Nevertheless, it possesses all 

 the essential properties and characters of vitality ; it is produced 

 from a body like itself; it is capable of assimilating nourish- 

 ment, and of exerting movements. Nay, more, it can produce 

 a shell ; a structure, in many cases, of extraordinary complexity 

 and most singular beauty (Fig. 2, D). 



That this particle of jelly is capable of guiding physical 

 forces in such a manner as to give rise to those exquisite and 

 almost mathematically-arranged structures being itself struc- 



