340 The Parasites of the Cockroach. 



our knowledge of the nature and manner of encystation is 

 derived. 



Y/hen the little cells escape froni the cyst, they are of an 

 elongated, doubly-conical form, in the earthworm bearing a 

 strong resemblance to the Diatom Navicula — hence they have 

 been called pseudo-JSTavicuk-e (Figs. 6, 7) . In the case of the 

 Gregarina Blattce, the cysts appear to escape from the body of 

 the insect into the ground before the pseudo-Naviculaa emerge : 

 but in the earthworm the little spindle-shaped cells may be 

 seen floating about in great numbers. They, too, then pass out 

 into the ground ; and, when there, some are sure to be swal- 

 lowed by an unsuspecting worm, or, in the case of G. Blattce, 

 by a greedy cockroach. The changes which they then undergo, 

 after being retaken into the interior of their hosts, are not well 

 known ; but in the earthworm they seem to become flaccid and 

 amcebiform (Figs. 8, 9), and then gradually develope into the per- 

 fect Monocystis Lumbrici. So much for the changes which the 

 Gregariniclge are subject to. The Gregarina Blattce is rarely 

 seen encysted, but has another curious habit which is sure to 

 be observed. Two hang together, with the head of one to the 

 tail of the other; that is, the smaller cell opposed to the larger 

 cell, as in Fig. 3. The parasite varies in shape, sometimes 

 being very much distended with its granular contents ; at other 

 times constricted in the middle, or looking like a representation 

 of a stone preserve-bottle. (See Figs. 1, 2.) The Gregarina 

 Blattce may be preserved as a microscopic object, by mounting 

 in a very shallow cell, in stiff jelly, to which an antiseptic has 

 been added. 



Infusoria. — Hastening about among the other contents of 

 the stomach, and stopping only occasionally to swallow a minute 

 piece of undigested matter, numerous individuals of a species 

 of Infusoria may be seen. These animalcules have never yet 

 been described in England, though they seem to be very plen- 

 tiful in the intestine of the cockroach. They were, however, 

 named by Dr. Leidy, of Philadelphia, some years since, who 

 also found a species very similar to this one in one of the Myria- 

 pods, Jtdus. The writer has lately discovered two new species 

 of this genus in other insects, w r hich he hopes shortly to describe. 

 The name of the genus which Dr. Leidy formed for these little 

 parasites is Nyctotherus ; the species which is found in the cock- 

 roach being the N. ovalis, whilst that of the centipede is 

 JST. vclox. 



Like all true Infusoria, they possess a mouth, but no aim I 

 aperture or alimentary canal. The animal consists simply of a 

 transparent sac, longitudinally striated, and furnished with 

 numerous cilia. The sac is filled with a clear, dense fluid 

 matter, in which float particles of food, drawn into the mouth 



