274 ERNEST WARRKN. 



blood-siiius, also in the superficial substance of the testis 

 itself. 



A remarkable circumstance in connection with fixation 

 should be noticed here. Encysted animals, whether adult or 

 developing, when fixed in corrosive and acetic, generally con- 

 tained a large quantity of gas between the cyst-wall and the 

 body of the animal, and it was accordingly impossible to 

 properly embed them in paraffin until the gas had been 

 expelled by pricking the cyst in several places. Specimens 

 fixed in Flemming's solution did not exhibit the same diffi- 

 culty; it would seem that this reagent acts in such a manner 

 on the cyst-wall that it remains permeable to the gas, while 

 corrosive sublimate renders it impermeable. Whether the 

 gas is normally formed by the parasite, and in the natural 

 state it slowly diifuses through the cyst-w^all, or Avhether the 

 reagents themselves acting on the body or cyst-wall produce 

 the gas, 1 am unable to state. It may be mentioned in this 

 connection that I have frequently observed the presence of 

 large bubbles of gas in the arteries of the crayfish. A. Willey 

 has observed a similar phenomenon in the blood-vessels of 

 the pearly nautilus. 



The crayfish was of Continental origin, and probabl}- it 

 came from Germany ; it was my sole source of material for 

 the present paper. I have been unable to find another 

 infested animal, although since the investigation was com- 

 menced I have examined at least a hundred specimens. 



Life-History of the Species. 



The life-history of D. cirrigerum, v. Baer, is very obscure. 

 The animal was first observed encapsuled in the muscles of 

 the crayfish by v. Baer ^ in 1827. Twenty years earlier, in 

 1808, Rudolphi^ found the trematode D. isostomum, Rud., 



' Baer, K. E. von, "Beitrage zur Kemitniss der niederen Tliiere" ('Nov. 

 Act. Acad. Caes. Lcop. Carol.,' torn, xiii), 1827. 



- Rudolphi, C. A., " Eutozoorum sive vermium iutestiiialum liistoria 

 iiaturalis," vols, i and ii, Ainstelod., 1808-9. 



