48 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 123 



efferent ducts (ed) unite in each testicular segment to form the deferent 

 ducts (dd), which enter a glandular organ, the spermiducal gland 

 (sg) . The deferent ducts may enter the ental end of the spermiducal 

 gland, with or without a previous thickening of the ducts, forming 

 deferent lobes of the gland (dl), or they may enter the gland near its 

 midlength. In some genera, an accessory gland, the prostate (pr), 

 is given off as a blindly ending sac, at the ectal part of the spermiducal 

 gland, where it narrows to form the muscular ejaculatory duct (ejd). 

 The latter, in turn, joins the bursa (b), the muscular eversible sac 

 (in the species considered here) enclosing the penis in its ental portion, 

 which may be considerably elongated (as in Ankyrodrilus) or a short, 

 pyriform organ (as in Cambarincola) . Of these components of the 

 male efferent apparatus, the spermiducal gland is always present but 

 may vary in shape, in the presence or absence of deferent lobes and in 

 the point of entry of the deferent ducts; the prostate may be present 

 or absent and, if present, may be histologically similar to or different 

 from the spermiducal gland and of varying proportional lengths and 

 diameters; the ejaculatory duct may be either present or absent and 

 of varying lengths, and the bursa of varying shapes. The other male 

 parts exhibit little variation of taxonomic importance. 



The female system is much simpler in arrangement and composition. 

 There is little variation in the arrangement of the ovaries and ovipores 

 in segment VII. The spermatheca (fig. 18) in segment V is an un- 

 paired sac (but bifid in Bdellodrilus) that may vary from species to 

 species in such features as the length and diameter of the ectal sperma- 

 thecal duct, the diameter and length of the spermatozoa-storing 

 spermathecal bulb, and the presence or absence of an ental process. 



Key to Branchiobdellids 



1 Body terete 2 



1' Body depressed, at least in part 9 



2(1) With bifurcate spermatheca; without prostate . Bdellodrilus illuminatus 



2' Spermatheca not bifurcate; prostate present 3 



3(2') Trunk segments III, IV, V, and VIII with fanlike dorsal projections. 



Pterodrilus alcicornus 

 3' Trunk segments without dorsal projections . . Cambarincola . . 4 



4(3') Jaws similar in size and shape, both upper and lower jaws with odd 



number of teeth 5 



4' Jaws dissimilar in at least shape, upper jaw with odd number, lower 



jaw with even number of teeth 7 



5(4) With peristomial tentacles, dental formula 5/5 C. fallax 



5' Without peristomial tentacles, dental formula may or may not be 



5/5 6 



6(5') Prostate histologically similar to spermiducal gland, spermiducal 



gland with deferent lobes, dental formula 5/5 . . . . C. branchiophila 

 6' Prostate and spermiducal gland histologically dissimilar; dental 



formula often 3/3 C. holostoma 



