PHYSIOLOGTCAL DEGENEEATION IN OPALINA. 635 



Description of Degeneration in Opalina. 



Having cleared the ground by describing tlie ordinary 

 course of events preceding gamete formation, I will now 

 pass on to a description of the physiological degeneration of 

 the forms whose usual destiny is to encyst. 



Two different kinds of degenerative changes may be distin- 

 guished — the one caused by removal from the host, the other 

 within the host. The former is much the more rapid, and is 

 easily induced at any time. Degeneration results from drying, 

 from increase in the number of bacteria, and also doubtless 

 from lack of food, and increase of metabolites. The entire 

 organism simply decomposes, often after first throwing out 

 its nuclei in fragments. It is the second kind of degene- 

 ration — that within the host — with which I am here con- 

 cerned. 



In nature, as we have seen already, the encystation of 

 Opalina is contemporary with the sexual activity of its host. 

 The set of degenerative changes which I am about to describe 

 took place when the ordinary activities of the host animals 

 were modified by captivity and starvation. Frogs, as is Avell 

 known, can endure starvation for many weeks. But the con- 

 tained Opalina3, apparently, cannot do so — at all events 

 at their encystation period. Starvation is, I believe, the 

 determining factor in their degeneration. Other causes, 

 which materially influence degeneration in the organisms 

 when removed from their host — such as change in reaction of 

 the medium, drying, increase in the number of bacteria, etc. 

 — do not appear to come into play. For after lengthy starva- 

 tion the rectal contents of the frogs and toads examined con- 

 sisted of only a small quantity of a clear, mucous fluid, 

 alkaline in reaction, and containing but few bacteria. It was 

 in cases such as this — where starvation of the host had some- 

 times lasted for at least two months — that the most advanced 

 stages in the degeneration of Opalina were encountered. 

 My observations extend over a period from the middle of 



