July i8, 1907J 



NA 1 URE 



271 



THE NATURAL HISTORY OF THE CEYLON 

 PEARL BANKS.' 



PROF. HERDMAN is to be congratulated on the 

 completion of his report on the pearl fisheries 

 and marine biology of Ceylon. It fills five large 

 volumes, which, besides containing much information 

 of direct practical importance in regard to pearls and 

 pearl fishing, form a broad and firm basis for further 

 study of the biology of the Ceylonese region of the 

 Indian Ocean. The report speaks volumes as to Prof. 

 Herdman's genius as a collector — we doubt if anv 

 single worker ever made such large collections over 

 the whole field of zoology in so short a time ; he has 

 also done his share of the descriptive studies, and he, 

 along with Mr. HornoU, is responsible for the parts 

 that deal directly with the pearl oyster itself. 



It is verv interesting to find that since Prof. Herd- 

 man's e.xpedition tliere have been four successive fat 

 years of pearl fishing — the most profitable, so far as is 

 known, that have ever been. In 1905, eighty-one and 

 a half millions of oysters were fished, and the revenue 

 brought in was upwards of two and a half millions 

 of rupees ; in 1906, more than sixty-seven millions of 

 oysters were fished, and the total proceeds amounted 



the deposition of successive layers of pearly material 

 within an epithelial sac. It seems that the grain-of- 

 sand method is occasionally found operative in the 

 causation of true pearls, and it is possible that some 

 of those that appear to have no nuclei may have been 

 deposited around very minute inorganic particles ; 

 some pearls not of the finest quality are probably 

 formed as calculus-like growths independently of 

 known parasites; but most and the best pearls are 

 de]x>sited around the larva of a Platyhclminth. In 

 the Ceylonese pearl oysters (Margaritifera vulgaris) it 

 seems likely that the parasite is a larval Tetrarhyn- 

 chus. Apart from pearly excrescences on the interior 

 of the shell, due to the irritation caused by Clione and 

 other boring animals, the authors distinguish (i) 

 ampullar pearls, where the nucleus and resulting pearl 

 lie between the shell and the body, or in an ampulla 

 of the ectoderm projecting into the mantle; (2) muscle 

 pearls, formed around minute calcareous concretions 

 (calcospherules) near the insertions of the muscles ; 

 and (3) cyst pearls, formed around encysted parasites. 

 .-\s to the proposal to secure artificial infection of 

 oysters, the authors think that this is probably quite 

 unnecessary on the Ceylon pearl banks. There seem 

 to be plenty of parasites to go round, and every 



1 lltrdmaiii, Dakin. Na 



to 1,385,000 rupees. This should surely convince the 

 Philistines that there is something in biology after all ! 

 Prof. Herdman predicts a moderate fishery for this 

 year, and a good fishery for 1908, adding that " after 

 1908 the prospects depend upon further careful scien- 

 tific inspecting, transplanting and culching, upon the 

 lines which have been laid down in successive sections 

 of the report." As is well known, the fisheries have 

 been leased by the Government to a company, and it 

 is a matter for congratulation that Mr. Hornell is 

 retained on the spot, and that, in terms of the lease, 

 the necessity for a scientific treatment of the pearl 

 banks during the next twenty years has been duly 

 recognised and provided for. 



Vol. V. begins with an interesting essay on pearl 

 production. The authors (Herdman and Hornell) 

 examine the three main theories — (i) that the pearl is 

 the result of a reaction to a grain-of-sand irritation, 

 (2) that the pearl is a pathological secretion, and (3) 

 that the stimulation caused by the presence of a 

 parasitic worm, which acts as a nucleus, results in 



1 Report to the Government of Ceilon on the Pearl Oyster Fishetie? of 

 the Gulf of Manaar. By W. ,\. Herd.nan, D.Sc, F.R.S., P.I-.S., with 

 Supplementary Rep.^rts on the Marine Fiiijlogy of Ceylon by Other Natur- 

 ali^ils. Part V. Pp. viii+j52; 3= plates. (Lontim: Published at the 

 request of the Colonial Government by the Royal Society, igo6.) 



NO. 1968, VOL. 76] 



pearl oyster in the Gulf of Manaar, or, for that 

 matter, around the coast of Ceylon, runs a fair chance 

 of becoming infected. It is to be hoped that further 

 investigation will make our knowledge of the pearl 

 parasite and its life-history more precise. 



In their report on Cestodes from Ceylonese fishes, 

 Messrs. A. E. Shipley and J. Hornell have some notes 

 on Tetrarhynchtis unionijactor, which they described in 

 vol. ii. Some of the larval forms entering the oyster 

 arrive in the mantle and other tissues, acquire an 

 ectodermic sac, and there encyst, finding " a costly 

 grave in the developing pearl." Others reach the 

 alimentary canal, and, after growing there, encyst on 

 the outer surface of the intestine. " They are too big 

 for enclosure in a pearl, and they can wait without 

 anxiety for the advent of their second host {Rhinoptera 

 javanica), within whose intestine they rapidly become 

 sexually mature." 



The late Prof. M. Stossich made notes on a few 

 Nematodes in the collection, and Dr. Max Liihe de- 

 scribes seven new species of Treniatodes from fishes. 

 The first part of the volume ends with a very valuable 

 general summary of practical conclusions and recom- 

 mendations, which we may hope will find application 

 not only in Ceylon but elsewhere. One cannot but 



