196 ISAO IIJIMA. 



pp. 167-168) have slated that the head of one individual is 

 turned towards the posterior end of the other, in such a 

 manner as to render possible reciprocal fecundation. John- 

 son, according to Moquin-Tandon (No. 6, p. 168), asserts 

 that the process is the same in Nephelis as in Hirudo. 



According to Ebrard (No. 9, p, 102), the two individuals 

 {H. medicinalis) always have their heads turned in the 

 same direction, so that, if both individuals are fecundated, 

 they must be so successively, and not simultaneously. 

 Other observations of Ebrard make it probable that only 

 one individual is fecundated during a single copulation. 

 This accords with my observations on Nephelis which are 

 as follows : 



The anterior portions of two individuals, attached by 

 their suckers to the glass-vessel near each other, are spi- 

 rally entwined in such a manner that the ventral surfaces of 

 their genital bands are always brought into apposition. 

 They maintain this position for a considerable time, now 

 and then changing the direction of their winding, and relax- 

 ing or tightening their hold. Sometimes the act is of short 

 duration, and two or three times renewed at short intervals. 

 At other times, and when disturbed, the act ceases alto- 

 gether, or else they combine with other individuals. It is 

 evident that there can be no reciprocal fecundation while 

 the leeches are coupling in the position above described. 



As there is no intromittent organ it is probable that the 

 male-orifice with its prominent muscular lips clasps the 

 female orifice, while the spermatozoa are forced onward by 

 the action of the ejaculatory organ. 



I am unable to say precisely at what time of the year 

 copulation begins ; but I found spermatozoa in the ovaries of 

 one leech on the 20th of February, for the first time in this 

 year. The act of coupling, so far as my experience goes, 

 takes place almost always in the morning. 



Ahiiormal Copulation. — I have often found individuals 

 with a small, two-horned, whitish object adhering to some 

 portion of the genital band. The position of this cornuous 

 body was always on or near the genital band, sometimes on 

 the dorsal surface, sometimes on the extreme margin, but 

 more frequently on the ventral surface than elsewhere. It 

 consisted of two thin-walled bottle-shaped tubes (ca. "5 mm. 

 long), the broader ends of which were inserted, close to each 

 other, into a small disc-like portion. This portion, the 

 margin of which presented a villiform appearance, was 

 partially embedded in the epidermis. Around the disc was 

 a discoloured area, which proved to be, on examination of 



