430 MR. GEOFFREY W. SMITH ON 



put straigbt, and the peculiar orientation of the parasites satisfactorily 



cleared up. 



The specimen of Lernceodistus munidce (= Triangulus munidce) found by 

 Professor Herdman is figured from two aspects on PI. 38. figs. 1 & 2. 

 The surface on which the mantle-opening {op.) is situated (fig. 1) is applied 

 to the thorax of the Manida when the tail is bent in its natural situation ; 

 the surface depicted in fig. 2 is applied to the abdomen of the host. The 

 peduncle (p.) by which attachment is effected is in a deep excavation of the 

 body, and the mantle is thrown into several pronounced folds. The mantle- 

 opening is asymmetrically placed on the lower right-hand corner, as shown in 

 fio-. 1, op. The only other features which can be observed from the outside 

 are the broad surface of the mesentery (w.r., fig. 1), which passes from the 

 peduncle to the opening, and the much narrower hinge of the mesentery 

 (m.l., fig. 2) upon the other side. 



In my previous account of Lernceodisciis these two hinges of the mesentery 

 were called anterior and posterior hinges respectively, as it was my view that 

 the loner axis of the body passed through the long axis of the mesentery, but 

 this is Incorrect, as Kollmann has shown, and we should call the longer 

 mesentery, passing from peduncle to near the opening, the right mesentery, 

 and the smaller mesentery on the other side the left. 



The disposition of the internal organs is shown in the diagrams figs. 3 & 4. 

 In fio-. 3, which is a transparent diagram of fig. 1, it is seen that the openings 

 of the testes are situated one on each hinge of the mesentery, the right testis 

 ir.t.) upon the edge of the large mesentery, the left testis il.t.) upon that of 

 the small mesentery behind. Both testis-ducts open backwards into the half 

 of the mantle-cavity turned away from the mantle-opening. The mistake 

 which was made in my earlier account of Lernceodisciis consisted in figuring 

 the left testis as opening on that edge of the left mesentery which is turned 

 towards the mantle-opening, and in the opposite direction to the duct and 

 opening of the right testis. The position of the testis-openings shows that 

 the lefr-hand part of fig. 3 is morphologically posterior and the right-hand 

 part anterior, while the mid-dorsal axis passes through the peduncle at 

 right angles to the long axis of the mesentery. The nerve-ganglion («.) is 

 situated on the large right mesentery, and the two oviducal openings are 

 placed on the visceral mass on either side of the mantle-opening. 



Fio-. 4 is a dingrammatic view looking down on the peduncle and on to the 

 mesenterial or dorsal side of the animal. Here is seen the smaller left 

 portion of the mesentery and the larger right portion stretching to near the 

 mantle-opening. The two testes are seen opening posteriorly to right and 

 left of the peduncle. The nerve-ganglion (n.) and the two oviducal openings 

 are seen situated on or near the right expansion of the mesentery. 



Before ooino- on to explain the peculiar asymmetrical disposition of these 

 organs, a comparison may be made between this condition in L, munidce and 



