Parasites of the Cuchle and Muaseh 141) 



for parasitic Trcniatodes, in the li()|)o of l)eing able to fill up 

 some of the yaps in tlic lit'e-iiistory of the pearl-fonniii,;^ 

 Distoniid of the mussel. The life-history of this parasite 

 {Leucit/wdemlrium soinaleria) has been almost completely 

 uorketl out by Dr, II. Lystcr Jamcsou^. At Picl he loinid 

 the sporocyst sta;^e in the mantle of the cockle close to the 

 anterior border of the anterior adductor muscle. At IJillicrs, 

 however, he found the same st;ige <jc(:urrin<^ in Tapes deius- 

 satus. From this we may conclude that the host harbouring 

 the sporocyst stage is not cunstaut, but varies accorduig to 

 lociility. 



Mr.' A. J. II. Russell, :M.A.t, at St. Andrews in 1902 

 (Ai)ril-July) examined a considerable number of both large 

 and small mussels from the beds at the mouth of the Eden. 

 He found pearls in 45 per cent, of the laige, and 21 per 

 cent, of the small mussels. These numbers fall short of 

 those obtaiucd by Dr. Jameson, who found almost every 

 8])ecimcu infected. This is probably due to the comparative 

 unsuitability of the locality. JNIr. Russell ap|)areutly did 

 not determine whether the parasite causing the pearl- 

 iormation in the E<\cn mussels was the same as that 

 described by Jameson, but, assuming this, I sought for the 

 sporocyst stage ill the cockle. During three months (May- 

 July) several hundred cockles were examined and in no case 

 were sporocysts present in the positions indicated by Jameson, 

 nor, indeed, in any part of the mantlc-cdge. 



Later, however, in examining the other organs of the 

 cockle, I met with sporocysts containing ecrcarite closely 

 re.^embliug those discovered by Jameson in Tapes. They 

 occurred in one well-defined, somewhat oval-slia[)ed mass 

 (PI. IV. fig. 1), situated in the middle line dorsally just over 

 the posterior bordiT of the liver, but separated from that 

 organ by a short distance (1-2 mm.). Tliey could be best 

 seen by removing the cockle entirely from the shell and 

 looking down on it from above. The mass then appeared 

 whitish, semiopaquc, and of a somewhat soft consistency, 

 \Vitliin it the individual sporocysts appeared as yellow sj)ots 

 of various sizes. The dimensiuns of the mass were in some 

 cases as large as 4 mm. x 3 mm. The oceurrcnee of the 

 sporocysts in this case is thus different from that observed 

 bv Jameson in Cardiuni and more nearly resembles the con- 

 dition in Tapes, for while in the latter large groups were 

 found, " there were only single, triple, or (piadruplc cysts " 

 iu the former. 



* IVoc. Zoul. 8oc. 1002, i. p. 110. 



t Ann. \: Mu-j. Nat. Ili-l. I'.)!!.", xi. p. .V)(), 



