674 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



diameter, the epididymis. This passes, without any enlargement into a 

 special sperm sac, into a short thick ductus ejaculatorius which, without any 

 apparent change in its diameter, is lost at once in the substance of the 

 prostate region of the atrium, into which it enters. The atrium is straight 

 not bent on itself and is chiefly remarkable for the great size of its 

 prostate region, which projects freely caudad beyond the point of entrance 

 of the ducts fora distance equal to more than one-fourth of the entire length 

 of the atrium, and reaches beyond ganglion XIX. This entire region is 

 covered with a layer of prostate glands. Anterior to the ducts the atrium 

 becomes a thick-walled muscular tube (the penis sheath) which is much 

 narrower than the prostate region and tapers somewhat to the external 

 end. It is unfortunate that no material was available for sectioning to 

 throw light upon the structure especially of the prostate end of the atrium. 



The female organs (Plate L, fig. 12) consist of a single ovary (that of 

 the left side being probably abnormally absent) lying in the posterior part 

 of somite XII. The right oviduct (the left being absent) enters a well- 

 marked glandula albuginea, within which it is somewhat coiled. It emerges 

 as the common oviduct, which is not very clearly differentiated from the 

 glandula, and enters the posterior end of the vagina, which is somewhat 

 enlarged but lacks a distinctly separated ovisac at this point. The entire 

 female organ is sharply bent on itself at the point where the- oviduct passes 

 into the vagina or uterus. The nerve cord passes to the left of the terminal 

 end of both atrium and vagina. 



In following Blanchard in placing this species in Semiscolex, I have 

 simply accepted his determination, as I have never had the opportunity of 

 dissecting any other species of that genus, and Kinberg's description is 

 itself insufficient. Verrill's Semiscolex grandis and Forbes' Semiscolex 

 terrestris are very different and both are true species of Htzmofiis, though 

 the absence of teeth in the former may be considered by some as a suffi- 

 cient basis for generic separation. Semiscolex variabilis also evidently 

 stands with Hcemopis in the distichodont division of the Hirudinidae, for, 

 although the alimentary canal differs from that of Hamopis and resembles 

 such a nephelid as Trocheta in the rudimentary jaws, valvular stomach and 

 all but absent caeca, it has the proportions of and can readily be derived 

 from that of Hczmopis. The reproductive organs resemble the latter genus 

 in the length of the vagina and penis sheath, the enlarged prostate, etc., 

 though in the absence of any special sperm and ovarian sacs on the ducts 

 it rather approaches Hirudo and its allies. 



