Pcirdsiks of the Cockle anil Afu.sscL I't') 



N(j rcdia or other iiitiriiudiatc sta;^e has as yet come und(;r 

 njy observation. 



Aji^ain, on examination of several other Lamellibranehiate 

 moUusks from the neighbourhood of the Eden, I found iu 

 the mnssel {Myti/tts cdttlis) and Mactra stultoruni the same 

 encysted parasites in the foot. They were as numerous in 

 the nuissel as in the coekh', and occurred in almost every 

 example; even in specimens measuring only 8 ram. as many 

 as half a dozen cysts could be counted in the foot. In 

 Mactra they were rarer. But in Mytilus and Mactra sporo- 

 cysts did not occur in the mantle, in the mid-dorsal line, or 

 in the liver. This would appear to be a proof that the sporo- 

 cysts in the liver, and those containing ccrcarire in the mid- 

 dorsal line, are stages of the same parasite, or, at any rate, 

 that they have no relation to the cysts in the foot. 



The antecedent stages of both these parasites are as yet 

 unknown. Examination of the mantle-cavity ot" the cockle 

 and mussel displayed numerous Infusor-like animals of 

 dilferent kinds, some of which may prove to be the Mira- 

 cidium larva *. 



EXPLAXATIOX OF PLATE IV.f 



Fi(/. 1. Diagram of cockle (removed from valves), showinp" situation of 



sporocyst mass (»».s.). A, liver; «.«., anterior adductor; jy.a., 



posterior adductor ; ?•., rectum. 

 Fi(/. 2. Pressure preparation of sporocyst mass, sp., the individual sporo- 



cysts; cer., cercaria. 

 I'll/. S. The cercaria. a.s., anterior sucker; e.s., eyes; p7i., pharynx; 



oes.f ce.-ophagus ; c.s., cuticular spines ; ex., excretory system ; 



div., intestinal diverticula; k.s., ;. lobular cells ; ^). v., posterior 



sucker ; ts., testis ; e.r.p., excretory pore. Cuticular spiuea 



omitted. 

 lu'i/. 4. Cyst from foot of cockle, showing' parasite coiled up inside. 



U.S., anterior sucker; c.s., ridge of supines; j)h., pharynx; 



e.i-., excretory system ; p.fi., posterior sucker ; e.v., excretory 



vesicle ; c, capsule. 

 I'll/, o. Cercaria from toot of cockle, fi.s., anterior sucker ; r.s., ridgo 



with spines; j)/i., pharynx ; c.s., cuticular spines; oes., (esophagus; 



(//^., intestinal diverticula ; />.«., posterior sucker ;/.<., tubule 



with tlame-Hugella ; e.v., excretory system; e.v., excretory 



Tesicle ; e.i-.p., excretory pore. Cuticular spines omitted. 

 I'll/. 0. Adult from intestine of oyster-catcher. Letterinjr same as in 



fig. o. 

 I'll/. 7. Sporocyst from liver of cockle, ph., pharynx; ^.5., eve-spots ; 



c, cilia; rt, undivided cyst; b, cyst, later stajje ; of, cyst cou- 



tainin)^ daughter-sporocysts ; il.s., danghter-sporocyst. ' 



* I should like to note here that in the mantle-cavity of the cockle 

 pwaruis of a spi'cies of Infusor of the genus Trivhuitina occiirrt'J. Tliey 

 were found both swimming about free and adhering to the maiUle and 

 foot. 



t I have to thank my friend Mr. D. D. Craig, M.A., for prepnriuir 

 the drawings which accompany this ])iii>er. 



