98 CEYLON PEARL OYSTER REPORT. 



anterior end of the body. Posterior sucker oval, with a longitudinal diameter of 

 2 "3 millims. to 2*6 millims. and a broadest transverse diameter (a little before the 

 middle of the sucker) of 2'1 millims. to 2*4 millims., with three pairs of hooks very 

 similar in form and arrangement to those of Benedenia hendorffi (v. LINST.), and with 

 four pairs of notches on the hinder half of its margin, due to the insertion of muscular 

 fibres, the third of these notches just behind the third pair of hooks. 



Mouth behind the plane of the hinder margin of the anterior suckers ; oesophagus 

 wanting. On the cerebral ganglion are two pairs of eyes ; the posterior eyes a little 

 larger than the anterior ones and directed forwards and outwards, the anterior eyes 

 directed backwards and inwards. 



Genital openings on the left lateral edge of the body, near the anterior end, by the 

 side of the anterior sucker ; the opening of the vagina just behind the common genital 

 pore. Testes large, two in number, paired, irregularly round. Ovary large, elliptical, 

 with its longer axis at a right angle to the longer axis of the body, situated in the 

 median line, just in front of the testes and midway between the anterior end of the body 

 and the centre of the posterior sucker. Vitellarium extending from the anterior end 

 of the body, between the two suckers, to about the front end of the posterior sucker, 

 that of the two sides intermingling with each other both in front of the cerebral 

 ganglion and behind the testes. Paired yolk ducts directed transversely to the long 

 axis of the body, uniting together near the median line just in front of the ovary. 

 Unpaired yolk duct dilated to form a capacious yolk reservoir, situated in front of the 

 left half of the ovary. The thinner end of the unpaired yolk duct unites soon with 

 the oviduct, which arises from the middle of the anterior border of the ovary and 

 proceeds forward. The canal arising from the united oviduct and yolk duct runs 

 from about the median line to the left, undergoing several convolutions and opening 

 into the ootype, which lies in the same line with the left border of the ovary. It has 

 a characteristic rhomboid shape and is continued into the short uterus. The vagina is 

 exceedingly long (hence the specific name macrocolpa) ; it arises from the yolk 

 reservoir at its left border, and running on the left side of the body, outside the 

 ovary and the testes, turns in a varying level between the hinder border of the testes 

 and the front margin of the posterior sucker lateral and oral, and then proceeds orally, 

 almost in a straight line, to reach the left margin of the body, at about the level of 

 the hinder margin of the anterior suckers. Vasa efferentia relatively long, uniting with 

 each other on the left side of the ovary ; the vas deferens runs in an almost regularly 

 curved line round the left side of the ovary and yolk-reservoir, and forms a large, close 

 pack of numerous complicated convolutions between the ootype and the yolk-reservoir, 

 then turning tailwards in a curved line and entering the penis in about the median line, 

 a little in front of the ovary. Penis long, running in a curved line round the shell 

 glands, ventral from the curved end of the vas deferens, and oral from the right half 

 of the ovary, and entering into the very long genital atrium, which reaches the median 

 line just before the ootype. 



