THE ANATOMY OF M EO Ar.ATKACTUS— KE8T1CVEN 145 



Vanstone only incntiuns one "bile" duct, whereas in Megala- 

 tractKS there are two. In the two species of Fuhus described by 

 Haller,* there are two ducts, but they are fused into one near 

 the stomach, so that there is only the one orifice, t 



I know of no extended description of the vascular system of a 

 Gastropod with which one may compare the present. Perrier's 

 valuable memoir — "Sur I'anatomie et I'histologie du rein des 

 Gasteropodes Prosobranches "I — lias given to us details of the 

 vascular system affecting the nephridium of the numerous types 

 he studied. The earlier memoir by Haller^ is not so extensive, 

 and I have, therefore, confined nij' comparison to that of the 

 French writer. 



The arrangement and origin of the nephridial veins in 3Iegala- 

 tractus do not find an exact parallel in any of Perrier's examples, 

 yet, on page 156, he gives the following general definition which 

 includes our example. The definition is in section v. : " Rein 

 proprement dit. Son irrigation. — Sur la surface libre de cette 

 masse spongieuse se voint presque partout des vaisseaux sanguins, 

 abondamment ramifies, et constituant un reseau vasculaire de 

 la plus grande richesse. Ces vaisseaux naissent d'un ou de 

 plusieurs troncs, dont les principaux partent du sinus abdominal 

 anterieur, que nous avons vu exister pres du rectum. 



" D'autres branches de moindre importance peuvent venir des 

 autres sinus veineux, soit de la masse visceral du tortillon, soit de 

 la cavite generale anterieure. 



" Ce reseau interieur de vaisseaux constitute le synteme afferent 

 du rein, comme pemettent de la conclure ses connexions avec les 

 sinus de la cavite generale." 



He then (p. 157) proceeds to describe the efferent veins. This 

 part of the definition, however, is not applicable, no efferent veins 

 of the type he describes being present in our first species. The 

 nephridium was in a sutficiently good state of preservation to 

 allow me to speak definitely on this point. 



The form of the nephridium, and the arrangement of the 

 afferent veins on its internal surface in Buccinuni, resemble 

 closely what has been found in Meg alatr actus, but the origin of 

 the veins differs. The following is Perrier's|| description of the 

 afferent system : — 



" Comrae toujours, dans le voisinage du I'ectum, et du pericarde 

 se trouve un vast sinus sanguin, faisant communiquer la cavite 

 generale du corps proprement dit avec les lacunes de la masse 

 visceral du tortillon. C'est de ce sinus, le sinus abdominal 



* Haller — Loc. cit., p. 161. 



t Haller — Loc. cit., figs. 18 and 20b. 



X Perrier— Ann. Sci. Nat., (7), viii., 1889. 



§ Haller— Morph. .Jarb., xi., 1886. 



II Perrier — Loc. cit., pp. 252-3. 



