The Parasites of the Cockroach. 339 



placed under the microscope, they have the appearance drawn in 

 Figs 1, 2. These are the Gregarina Blattce. The Gregarinida 

 are a group of animals first discovered by Leon Dufour, the 

 celebrated entomologist. They inhabit the alimentary canals 

 of insects, Annelides and some Crustacea. In structure, 

 though larger in size, they are nearly as simple as the Vibrio. 

 A simple sac, which is very obscurely striated, and is highly 

 elastic and moveable, encloses a mass of minute granules, 

 in the centre of which is a clear, transparent vesicle ; within 

 the vesicle there are generally a few irregular granules, one of 

 which is nucleated (Fig. 2a). In some species the sac is 

 divided into two portions by a thin partition ; one portion, 

 which is much the larger, containing the vesicle and surrounding 

 granules, whilst the other contains simply granules. This 

 smaller portion is, however, sometimes provided with a pro- 

 boscis, occasionally armed with little hooks, by which the Gre- 

 garina is attached to the walls of the intestine. The Gregari- 

 nida3 have thus been divided into two sections ; the one single- 

 celled and inhabiting Annelides and Crustacea, the other two- 

 celled, and found in Insects and Myriapods. The single-celled 

 division forms the genus Monocystis, a few species of which are 

 large, and provided with a proboscis, while the greater number 

 are minute and simple in form. The two-celled species form 

 the genus Gregarina proper, and are more frequently provided 

 with anterior prolongations of the membranous sac; though 

 the species inhabiting the Blatta happens to be destitute 

 of one. 



The Gregarinida have no mouths, and live by absorption 

 of the fluids of the animals they inhabit. Their movement is 

 sluggish but constant, unless they are distended with granules, 

 as is sometimes the case, or about to undergo the process of 

 encystation. The process of encystation is the mode by which 

 the Gregarinidae are propagated. There appears to be no true 

 sexual reproduction ; but the following process takes its place : — 

 Two Gregarina?, or a single one, become quiescent, and are 

 then invested with a structureless, transparent cyst or covering, 

 which completely envelopes them (Fig. 3a). In the course of a 

 short time, the two animals, if there are two, become confused 

 into one dark, brown mass, which eventually splits up into little 

 nucleated cells. These remaining inside the cyst, assume an 

 elongated form, and at length emerge from their covering. 



The changes which take place when the Gregarinidae are 

 encysted have been well observed in the Monocystis Lumbrici, 

 which is very plentiful in the common earthworm. In parts of 

 the reproductive organs of this Annelide hundreds of these 

 Gregarinida? may be seen in various stages of encystation ; and 

 it is from the observation of these that the entire amount of 

 vol. vi. — no. v. z 



