THE PKAiir. FrsiiKijii'.s ok ckvi.on. 491 



In connection with ciiKivnlioii and liansplantation, there are vari- 

 ous points in strncliirc. i'('|)r()(lucli<)ii. life-history, growth and liahits 

 of tlie 03'stor which we had to deal willi. and some of which we were 

 al)U' to dcterniino on Ihc haid<s, while others haxc heen the subject of 

 Mv. Ilorncirs work since, in the little niai-ine lahoratorv w'> estah- 

 lished at Galle. 



Although (Jalle is at the opposite end of the ishind form the pearl 

 l)aidx:s or JNfanaar, it is clearly the hest locality in Ceylon for a marine 

 lahoratorv — both for general zoology and also foi- working at pearl 

 oyster j)r()blems. T>iittle can be done on the sandy exposed shores of 

 Afanaar island or the Tiight of (V)ndatchy — the coasts op])osite the 

 pearl banks. The tisheries take place far out at sea, fi'oni 10 to 20 

 miles oft' shore; and it is clear that any natural history work on the 

 pearl banks must be done not from the shore, but as we did, at sea 

 from a ship during the inspections, and can not be done at all during 

 the monsoons because of the heavy sea and useless e.\i)osed shore. 

 At such times the necessaiy laboi-atory work supplementing the 

 previous observations at sea can be carried out much more satisfac- 

 torily at Galle than anj'where in the Gulf of Manaar. 



Turning now from the health of the oyster population on the 

 " ])aars," to the subject of pearl formation, which is evidently an un- 

 healthy and abnormal ])i'oc(>ss, we find that in the Ceh^on oyster 

 there are several distinct causes that lead to the production of pearls. 

 Some pearls or pearly excrescences on the interior of the shell are due 

 to the irritation caused by boi-ing sponges and burrowing worms. 

 French writers have made similar observations in the case of Donax 

 and other Lamellibranchs; and Dubois (1901) has nioiv recently 

 ascribed the production of pearls in nuissels on the French coast, to 

 the presence' of the lar\a of Distomum margaritarum. Jameson 

 (1902) then followed with a more detailed account of the relations 

 between the pearls in Mytilus and the Distomid larva% which lie 

 identifies as Distonunu ( Urachycielium) sonuitcM-ia' (Levinson). 

 Jameson's observations were made on niiissels obtained partly at Bil- 

 liers (Morl)ihan), a locality- at which Dubois had also worked, and 

 l)artly at the Lancashire Sea-Fisheries marine labortoi-y at Piel in 

 the Barrow Channel. Finally, Dul)ois has just iiublished a further 

 note in which, referring to the causation of pearls in Mytilus, he 

 says: "En souuue ce que ce dernier [Garner | avait vu en Angle- 

 terre en 1871, je Fai retrouve en Bretagne en 1901. Quelques jours 

 apres mon depai't de I>illiers, M, Lyster Jameson, de Londres, 

 est venu dens la mr-nie localite et a confirme le fait observe par 

 Garner et par moi." But Jameson luis done rather more than that. 

 He has shown that it is probable (his own words are " there is hai'dly 

 any doubt ") that the parasite causing the pearl-formation in our 



