THE CEYLON PEARL-OYSTEll. 



277 



plates, the concentric stratification of tlie majority of which 

 never occur.s in a Treuiatode nucleus, and could hardly be expected 

 in a Cestode. 



Text-fig. 3.3. 



^\ 



A llytihis pparl, from Foulntn-, near I'ifl, Lancasliive, witli a Treinatode nucleus: 

 A, uxaniiiiud entire in oil of cloves, after decalciticatioii ; B, the same in section. 

 In A the oral sucker and digestive cteca of the worm are distinctly visible. 

 In 15 the internal anatomy is still preserved. cu., cuticle; sp., spines on 

 same ; dig., digestive ciecum ; skr., ventral sucker ; at rfand q arc dark masses, 

 which may well represent the remains of the yolk-glaiids and gonads; 

 nnc, nacre. C, a, Mi/tihis pearl of non-Trematode origin, from Plymouth. 

 Here the nucleus is, as in many Ceylon pearls, a minute group of granules. 

 A X 20; B X 70; C X 20. 



As j\tr. Cyril Crossland, Marine Biologist to the Sudan Govern- 

 ment, is quoted by Professor Herdman (Report Ceylon Pearl 

 Fisheries, Pt. V. Pearl- Production, p. 3) as supporting the Cestode 

 theory, so far as M. valyaris in the Red Sea is concerned, I wrote 

 to him to ask him for further information. He replied, in 

 a letter dated JJecember 9th, 1911 :— "I never published any state- 

 ment that Cestode larvae caused pearl-formation in the Red Sea. 

 The evidence to my mind is in need of revision. In all cases the 

 first residt of excessive stimulation of the secretory epidermis of 

 the mantle is the formation of a dark brown horny material 

 [i.e. my amorphous substance.— H. L. J.]. How would this stain 

 in sections, and is it cellular like the horny material of the prismatic 

 layer ? If so, would not a shrunken nucleus of such material 

 resemble the dry remains of a Cestode ? This is a criticism which 

 I have had in mind several years, and have never put it to 

 the test." From this it is clear that Mr. Crossland, though cut 

 off from the possibility of applying modern laboratory technique, 

 has arrived at much the same conclusion as that which I am 

 elaborating in this paper. 



To summarise the supposed relation between Cestodes and 



