350 Parasites from the Zoological Gardens. 



At the upper or anterior extremity of the body we notice the 

 round oral sucker (a), which is almost as large as the ventral 

 sucker, or acetabulum (marked b). The mouth, properly so 

 called, is placed at the bottom of the oral sucker, and leads 

 into a small oval muscular cavity, which is termed the oeso- 

 phageal bulb (c), and this, again, directly communicates with 

 the two long, cylindrical, digestive tubes (d, d), which widen 

 out a little as they approach the caudal extremity of the body, 

 where they terminate in closed, rounded, cascal ends. This 

 arrangement constitutes the simplest form of alimentary appa- 

 ratus with which we are acquainted in the trematode parasites, 

 and, associated with the disposition of the two suckers as here 

 placed, it is eminently characteristic of the genus Distoma. 

 Immediately above, and in contact with, the ventral acetabulum 

 there will be observed a small, round papilla (e) ; this is in- 

 variably furnished with and usually exhibits two minute open- 

 ings upon it, which are respectively the orifices of the male and 

 female reproductive organs. One of these openings communi- 

 cates with that set of wide, tortuous tubes (/), occupying the 

 centre of the upper half of the body. The brown colour is a 

 natural appearance due to the presence of multitudes of mature 

 eggs (Fig. 3) which are crowded within this coiled uterine duct, 

 the latter being also connected by a narrow channel with the 

 ovary (g), and by two other minute ducts, passing, one on 

 either side, to the so-called yelk-forming glands. These last- 

 named organs form botryoidal masses on either side of the 

 body, and, though varying considerably both in extent and 

 arrangement, their presence is in a measure characteristic of 

 this class of parasites. The letters h h refer to these organs, 

 but the dotted lines have been prolonged by the engraver 

 rather too far inwards; the glands are coloured yellow. In 

 Fig. 4 the lid-like end of one of the highly magnified eggs has 

 been represented artificially burst open. The ova have a long 

 diameter of l-750th of an inch. The male reproductive orifice, 

 like the other, is not seen in the accompanying illustration, 

 but it communicates with the reproductive glands (k, Jc) by 

 the intervention of vasa deferentia, or channels of outlet, in 

 the usual manner. The true excretory system of vessels is 

 well marked in this fluke, and consists of two main trunks 

 (i, i) lying immediately in front of the yelk-forming glands ; 

 gradually increasing in size, and passing in a nearly straight 

 line downwards, they converge to meet at a point corre- 

 sponding with the centre of an imaginary line separating the 

 lower third of the body, and in this situation the common tube 

 sweeps round and between the reproductive glands in the 

 form of the letter s, after which it swells out into a contractile 

 vesicle (/), which opens externally by a very narrow outlet at 



