BULLETIN 120, UNITED STATES NATIONAL MUSEUM^ 



a cover-glass smear, material for study. Cover-glass smears killed 

 at once, Avithoiit drying, in hot corrosive sublimate-acotic acid solution, 

 in hot corrosive sublimate solution, or in Schaudiim's corrosive subli- 

 mate-absolute alcohol solution, give very satisfactory results. Dela- 

 field's hematoxylin, overstaining and reducing, is the most easily 

 and accurately controllable stain and gives on the Avhole the best 

 results. Borax-carmine, alum-carmine, Lyons blue, and many other 

 stains are satisfactory. With very thin species, and for the study 

 of the cytoplasmic spherules in any species, iron hematoxylin gives 



very clear results. The Opalini- 

 dae present no special difficulties 

 in preserving or staining, except 

 that stains v^hich color the cyto- 

 plasmic spherules obscure the nu- 

 clei in total preparations, except 

 of the flattest species. For micro- 

 scopic sections, the use of paraffine 

 imbedding with gelatine capsules 

 and Lefevre watch glasses is very 

 satisfactory.^ 



In collecting Opalinidae from 

 frogs and toads preserved in alco- 

 hol or formalin no real injury need 

 be done to the host. The rectum is 

 either axial or turned to the right 

 side. The upper end of the rectum 

 with the rudimentary caecum in 

 many species lies well up toward 

 the right arm. I have found a 

 boomerang-shaped cut on the ven- 

 tral surface most convenient (fig. 

 2). Care, of course, should be 

 taken, with museum specimens, not to cut the posterior cartilage ol 

 the sternum. The triangular flap of abdominal wall, released by 

 the incision, may be bent back, and there is abundance of room for 

 exploring the abdominal cavity and locating the rectum. When 

 found, this can be pulled out through the incision and its upper 

 portion slit open. The caecum is dorsal (fig. 1), so it is well to slit 

 the rectum on one side. I have found a narroAv section lifter, 3 mm. 

 Avide, the most convenient tool for taking out the rectal contents. 



The ventral abdominal incision does really no injury to the host 

 as a museum specimen. Indeed careful collectors usually open the 



Fig. 2. — Ventral surface of a frog. 

 The dotted line indicates the form 

 of cut through the abdominal wall 

 to give access to the anteuiou end 

 of the rectum. 



'■ See Metcalf (1909), p. 9. 



