280 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lu 



macerated mterna]ly. Sometimes thick or opaque specimens can be 

 utilized by turning the slide over and focusing on the other side of the 

 anunal, or by dissolving the balsam away in clove oil or xylol and 

 remounting. 



Very small animals, or those with complicated reproductive systems, 

 must sometunes be imbedded in paraffin and sectioned. Well-known 

 histological techniques, using a hematoxj^lin-eosin stain, suffice for 

 serial sections. I have found no advantage in staining specimens for 

 whole mounts. 



Often it will be found necessary to derive specific characters from 

 several specimens, there bemg few mounts in which aD the desired 

 details can be seen on a single animal. 



Taxonoinic Characters 



The taxonomic utility of various anatomical systems in the Bran- 

 chiobdellidae has been discussed in the literature at least four times. 

 Insofar as earlier workers were concerned, general body form and 

 shape of the jaws provided sufficient basis for the recognition of species, 

 an opinion which unfortmiately has survived in some quarters nearly 

 down, to the present time. That internal anatomy might furnish 

 characters of really fundamental importance was first intimated by 

 the still unsurpassed account of Bdcllodrilus illuminatus by J. Percy 

 Moore in 1895. Almost two decades later, EUis (1912) relied to some 

 extent on the form of the male reproductive systems in the diagnosis 

 of his Cambarincola macrodonta, but hi his subsequent work of 1919, 

 Ellis largely reverted to nonsexual characters in the definition of 

 genera and species. In this practice he was followed by C J. Good- 

 night, and not until 1949 was the study of reproductive morphology 

 revived by Perry C. Holt. Subsequent work by Holt, and that done 

 under his du-ection by the present investigator, has been predicated 

 upon the assumption that characters of the male reproductive systems 

 provide the most reliable indices of evolution within the group, and, 

 therefore, the best means for the definition of species and genera. 



Ellis (1919) devoted considerable attention to the form of the jaws, 

 the nomenclatm-e of their dentition, and their mode of evolution, as 

 well as to pharyngeal diverticula, mtersegmental septa, and form of 

 the gut. No further treatment of taxonomic characters appeared 

 until 1935, when Yamaguchi provided a detailed consideration of 

 various useful details, including the body form and ornamentation, 

 jaw structure, and the internal characters mentioned by Ellis. 

 Yamaguchi also discussed variations in the reproductive systems, 

 but not in as much detail as might be desired. 



Goodnight's monograph of 1940 reviewed the work of both EUis 

 and Yamaguchi, as well as several of theu* predecessors, and en- 



