T 36 MADRAS FISHERIES BULLETIN [VOL. XVI, 



In the nests of these pearls in a very early stage which I have 

 often examined, the columnar structure is extremely clearly shown ; 

 in optical section each pearl is seen as an oval body made up of 

 lines radiating from an almost imperceptible nucleus of the same 

 refractive index. The pearl-sacs of adjacent pearls are very prone 

 to coalesce both in this early stage, the calcospherule stage as 

 Prof. Herdman and I named it originally, and at a later date when 

 of larger size. In this way irregular pearls are formed. Usually 

 only one concentric layer of hypostracum is laid down, but more 

 may, rarely, be deposited. As a rule the next layers laid down 

 are composed of nacre, and in this way the pearl finally assumes 

 the normal appearance of a pearl, at least one of inferior quality. 

 Owing to the crowding together of these pearls as happens nor- 

 mally, mutual pressure adversely effects their shape. Frequently 

 they are found partially coalesced, as twin pearls ; more usually 

 they are irregular and mishapen in varying degree. They con- 

 stitute the bulk of the seed-pearls put upon the market. 



Very vigorously grown adult oysters, particularly those of 

 exceptional size, are prone to form nests of these muscle pearls ; 

 this is exactly what we would expect reasoning from the facts 

 stated above. In oysters of this description, the strengh of the 

 muscle fibres is exceptionally great and as a consequence dis- 

 lodgment of tiny particles of the hypostracal layer to which they 

 are attached and disturbance of the cells secreting this substance 

 are more frequent than in smaller and weaker oysters, where 

 muscular force is distinctly feebler. 



X.— CONCLUSIONS AND RECOMMENDATIONS. 



A.— CONCLUSIONS. 



The outstanding conclusions of supreme importance to which 

 my investigation of the records and natural characteristics of the 

 Tinnevelly and Madura pearl banks has led are that the banks 

 have latterly given inferior returns owing to — 



(a) The imperfections of the present methods of inspection, 

 and 



(b) Deficiency in the supply of divers when fisheries are held. 



