THE OPALINID CILIATE INFUSORIANS. 5 



Aentral abdominal wall before placing a frog or toad in the preserv- 

 ing fluid. In the 1,079 operations made upon the specimens in the 

 National Museum I injured externally but 2, and these only very 

 slightly, by tearing the incision open farther than intended. The 

 injury to the gut, however, is greater. Its folds are often disar- 

 ranged. In many of the smaller forms the rectal wall is delicate 

 and after it is slit open and the contents removed it collapses and 

 study of the natural structure of the upper part of the rectum would 

 afterwards be difficult in these operated specimens. In about 20 

 instances out of the 1,079 operations, the rectum broke at its junction 

 with the small intestine. These injuries, external and internal, in- 

 terfere not at all with the usual use of museum specimens and they 

 are on the whole so slight that they should hardly cause one to hesi- 

 tate to study museum material of species of Anura whose rectal 

 parasites are insufficiently known. Many museums have much ma- 

 terial very valuable for such study. We have no observations upon 

 the Opalinid parasites of Dyscophinae^ Dendrophrynisc'mae^ Amphi- 

 gnathodontinae, Hemiphractinae^ Genophryninae^ or Ceratohatrai- 

 hinae, and there are many genera of other families whose Opalinid 

 parasites are unknown. Section 8 of this paper gives a list of all 

 genera and species from which, so far as the author can learn, 

 Opalinidae have been reported. In this list only the starred species 

 indicate infection. Any genus or species not in this list, or in the 

 list and not starred, is not known to the author to harbor Opalinidae. 



In addition to the Opalinidae, the National Museum material gave 

 many infections of rectal Nematodes and nearly as many of Nycto- 

 thcnis and BaJantidium^ also some Discophrya and some Trematodes. 

 These have been or will be given to special students of these forms 

 for study. 



It is important to note that alcoholic specimens of Anura have 

 the parasitic Opalinidae far better preserved than do formalin speci- 

 mens. The latter seldom yield any Opalinids, though in specimens 

 which had the abdominal wall opened before preservation Opalinids 

 may occasionally be found, and rarely specimens not so opened may 

 yield Opalinids. A large percentage of the failures in my explora- 

 tion of National Museum Anura was undoubtedly due to formalin 

 preservation. Alcoholic material, on the other hand, if well pre- 

 served, shows the Opalinids, if present, in good condition. Often- 

 times nuclear structure may be studied and the chromosomes counted. 

 Even in very soft specimens of the Anura, to one's surprise, he often 

 finds the Opalinids well enough preserved for taxonomic study. 

 Fifty-five per cent alcohol, the strength usually used for Anura, gives 

 thoroughly satisfactory preservation of the Opalinidae, and it is evi- 

 dent that Opalinids so preserved maintain their form and remain in- 



