418 RECORD OF CURRENT RESEARCHES RELATING TO 



narrow white border bounding the edge of the mantle. In the adult 

 it disappears and is replaced by the tissue of the mantle. The long- 

 necked cells are transformed into ordinary epithelial cells, capable of 

 producing nacre. The pallial groove, on the other hand, is permanent, 

 but the glandular caeca which line the bottom gradually atrophy. 

 The consequence of this disappearance and atrophy is that a cicatrix 

 in the shell can no more be covered over by cuticle in this region 

 than in the other parts of the mantle, whilst this does takes place 

 when the animal is still growing. 



The function of the cutogenic organ is as follows. 



The glands of the pallial groove secrete mucus, perhaps that 

 substance which chemists have found associated with the calcareous 

 matter of the shells and have called conchyoline. 



The long-necked cells of the epithelial organ then deposit in the 

 membrane emanating from the pallial groove the granules which 

 they contain. The cuticle is the result of this double secretion. 

 When a young Helix adds to its shell, it applies the edge of the 

 mantle closely to the last formed part so that the cutogenic apparatus 

 borders this part. Above the groove there soon appears a membrane 

 destitute of lime. The animal is so adherent to the shell, that it 

 does not react against slight irritations which, at another time, would 

 cause it immediately to withdraw. It can sometimes be killed in 

 this position, and interesting antero-posterior sections be obtained at 

 the same time of the apparatus and the cuticle in the course of 

 formation. In some of these sections, a streak of matter is seen pro- 

 ceeding from the groove and becoming impregnated above the 

 epithelial organ with granules escaping from the cells of the latter, 

 whose function would seem to be to consolidate the membrane 

 secreted by the glandular cseca. 



The turning out of the margin of the shell in the adult Helix is 

 explained thus : — After the atrophy of the epithelial organ the 

 portion of the mantle which it occupied sinks down and carries with 

 it the part of the cuticle which covered it. The anterior portion of 

 this membrane above the pallial groove, the level of which has not 

 changed, is thus raised and is soon lined on its internal face by 

 calcareous deposits. 



If a fragment of the fine membrane detached from the margin of 

 a shell in process of increment be examined, it is seen that the most 

 recent part is formed almost exclusively by the cuticle ; a little 

 further back this is lined with rows of spherical granules ; further 

 back still these granules form a continuous calcareous layer lining 

 the under surface of the cuticle. In a young Helix from which a 

 portion of the cutogenic apparatus has been removed, the exterior layer 

 above the mutilated part is formed in another way. Some little rods 

 of a calcareous nature appear first, which swell gradually at the two 

 extremities and take the form of wallets. By the addition of new 

 particles these wallets are transformed into sjiheres whose dimensions 

 augment by concentric deposits with radiating striae. These spheres 

 finally touch each other. The first calcareous layer is therefore 

 formed differently according as it is exposed or protected by the 



