60 MANUAL OF ZOOLOGY. 



rather lead us to place them in the neighbourhood of the 

 Infusoria. The presence of muscular fibres in the cortical 

 layer will also support the view that they should be associated 

 with the Infusorian animalcules. 



In spite of their exceedingly simple structure, the following very in- 

 teresting reproductive phenomena have been observed sometimes in a 

 single Gregarina without apparent cause, sometimes as the result of the 

 apposition and coalescence of two individuals the exact nature of the 

 process being in either case obscure. In some species conjugation is in- 

 variable ; in others it never occurs ; and it may take place either by anal- 

 ogous or by opposite extremities. The Gregarina or it may be two in- 

 dividuals which have come into contact and adhered together assumes a 

 globular form, becomes motionless, and develops round itself a structure- 

 less envelope or cyst, when it is said to be "encysted" (fig. 6, c). The 

 central nucleus then disappears, apparently by dissolution, whereupon 

 the granular contents of the cyst break up into a number of little rounded 

 masses, which gradually elongate and become lanceolate, when they are 

 termed " pseudonavicellse " (or "pseudonaviculse," fig. 6, d}. The next 

 step in the process consists in the liberation of the pseudonavicellae, which 

 escape by the rupture of the enclosing cyst (fig. 6, e). If they now find a 

 congenial habitat, they give origin to little albuminous or sarcodic masses, 

 which exhibit lively movements, and are endowed with the power of 

 throwing out and retracting little processes of the body which closely 

 resemble the " pseudopodia " of the Rhizopoda ; so that the pseudona- 

 vicella in this condition is very similar to an adult Amceba (fig. 6, f, g, h). 

 Finally, these amcebiform bodies are developed into adult Gregarina:. 

 It will be seen from the above that the formation of the pseudonavicellce 

 out of the granular contents of the body, subsequent to the disappearance 

 of the nucleus, presents a close analogy to the segmentation of the impreg- 

 nated ovum which follows upon the dissolution of the germinal vesicle. 

 In Gregarina gigantea of the Lobster the embryo is a little mass of sarcode, 

 quite like an Amceba except that it wants a nucleus and contractile vesicle. 

 It soon gives out two little contractile processes or arms, which become 

 detached and move about like little worms, when they are termed ' ' pseudo- 

 filarise," from their resemblance to free Nematoids. After a period of 

 activity, the pseudo-filarian becomes quiescent, shortens its dimensions, 

 develops a nucleus and nucleolus, and becomes an adult Gregarina. 



PSOROSPERMLT.. There occur as parasites on and within the bodies of 

 fishes certain vesicular, usually caudate, bodies, termed Psorospermice, the 

 exact nature of which is very problematical. According to Lieberkiihn 

 they occasionally give origin to amcebiform bodies, similar to those which 

 are liberated from the pseudonavicellae of Gregarinida. In this case they 

 should probably be regarded as the embryonic forms of some Gregarina. 

 By Balbiani, however, they are looked upon as properly belonging to the 

 vegetable kingdom. 



