GREGARINIDA, RHIZOPODA, SPONGIDA, AND INFUSORIA. ( J 



any longer those movements of which I spoke, and becoming 

 coated by a structureless investment, or " cyst" (Fig. 1, B). 



The substance of the body contained within the cyst next 

 undergoes a singular change. The central nucleus and the 

 vesicle disappear ; after a time, the mass breaks up into a series 

 of rounded portions and, then, each of those rounded portions 

 elongates, and, becoming slightly pointed at each end, consti- 

 tutes a little body which has been called a " Pseudo-navicella" 

 from its resemblance to the Diatomaceous Navieula or Navi- 

 cella (Fig. 1, C, D). Next, the capsule bursts and the Pseudo- 

 navicellm (Fig. 1, E, F) are scattered and passed out of the 

 body of the animal which they inhabit. Though, of course, a 

 great number of them are destroyed, some, at any rate, are 

 devoured by other animals; and, when that is the case, the little 

 particle of protein substance which is inclosed within the 

 Pseudo-navicella is set free from its shell, and exhibits much 

 more lively movements than before, thrusting out processes in 

 various directions, and drawing them in again, and, in fact, closely 

 resembling one of those animalcules which have been called 

 Amoehse (Fig. 1, H). The young Amoebiform Gregarina grows, 

 increases in size, and at length assumes the structure which it 

 had at first. That, in substance, is all that we know of this 

 lowest division of animal life. But it will be observed, there is 

 a hiatus in our knowledge. We cannot say that we know the 

 whole nature and mode of existence of this, or any other animal, 

 until we have traced it to its sexual state ; but, at present, we 

 know nothing whatever of this condition among the Gregarinm ; 

 so that in reasoning about them we must always exercise a cer- 

 tain 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 Gregarinw, 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 Gregarina may become encysted and break up into 

 Pseudo-navicellce seems to negative this analogy. 



But now, leaving this, I pass on to the next class — that which 



