170 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Purple of Dog-Whelk.* — R. Dubois has previously shown that the 

 purple of Murex brandaris is the result of the transformation of a sub- 

 stance which he called purpurine by a ferment which he called purpurase. 

 These substances occur in the purple gland, and, by their interaction, 

 give rise to unstable bodies whose change in various physical conditions- 

 results in the purple fluid. As Letellier has stated that this does not 

 hold true of Purpura lapillus, Dubois has repeated for this animal the 

 observations which he made on Murex, and finds that the same is true 

 in both cases. 



Relations of Kidneys and Gonads in Haliotis.f — R. J. Totzauer 

 finds that the two kidneys are quite separate, opening apart into the 

 branchial cavity ; that the rudimentary left kidney opens on a papilla, 

 without a proper efferent canal such as the right kidney has ; that the 

 left kidney is connected with the pericardium by a reno-pericardial 

 duct ; that the relations between pericardium, right kidney, and gonads, 

 correspond precisely to what Pelseneer has described for Fissurellidse and 

 Trochida?, except that in front of the communication between genital 

 duct and reno-pericardial duct, there is a second communication between 

 genital duct and right kidney, similar to that described in Parmophorus 

 intermedins by Tobler. 



5. Lamellibranchiata. 



Formation of Pearls. J — H. Lyster Jameson has studied this in 

 Mgtilus edulis and some other bivalves. The formation of a true pearl 

 is like that of the shell, except that a pearl is laid down in a closed sac 

 of the shell-secreting epithelium, imbedded in the subepidermal tissue 

 of the mantle and completely cut off from the outer epithelium itself. 

 Inside this spherical epithelial sac, the shell substance is laid down in 

 the characteristic concentric layers. Sac and pearl may be compared to 

 a human atheroma cyst. 



A sharp distinction must be drawn between true pearls and blisters, 

 or pearly excrescences of the shell lining, which are secreted by the outer 

 mantle epithelium to cover over foreign intrusions, &c. " Concretions,"' 

 again, are calcosphreritic bodies which have not a cuticular origin, but 

 seem to arise by free crystallisation in the mantle or other tissues. The 

 term " attached pearl " should be applied only to pearls which have 

 become secondarily fused to the shell by absorption of the intervening 

 tissues. 



Pearls naturally vary according to the animal and according to the 

 part of the mantle implicated. Thus, pearls formed at the margin are 

 composed mainly of periostracum, e.g. leathery pearls of Modiola modiolus, 

 while those which occur in the part of the mantle concerned in depositing 

 the prismatic substance are made up of concentric layers of rod-like 

 prisms, as in the brown pearls of Margaritana margaritifera. By far 

 the greater part of the mantle epithelium deposits nacre, and typical 

 pearls are of course nacreous. The material of the ligament is represented 

 in the black leathery pearls sometimes found in the dorsal wall of the 

 Australian Margaritifera maxima Jameson. 



* Comptes Rendus, cxxxti. (1903) pp. 117-S. 



t Zool. Anzeig., xxv. (1902) pp. 487-8. 



j Proc. Zool. Soc. London, 1902, pp. 140-66 (4 pis.). 



