l66 The Irish Naturalist. December, 



mould in the petrie-dish, which was covered by its glass 

 cap and laid aside in a desk to await developments. 



The eggs varied slightly in form and size. The majority 

 were globular, with a diameter of 4*5 mm. ; a few were 

 ellipsoidal, with a longer axis of 5-5 mm., or, say, one-fourth 

 of an inch. An outer filmy skin enclosed a dense layer of 

 what appeared to be minute, white granules, the two 

 forming a tenacious coat which enclosed a second filmy 

 skin containing the colourless, glairy, albuminous matter 

 destined for the nutriment of the embryo. Under a one-sixth 

 inch objective the white granular coating was resolved into 

 a dense layer of transparent crystals of the form known as 

 rhombohedrons, these crystals being free or aggregated into 

 small groups. In dilute nitric acid this crystal coating 

 dissolved with brisk effervescence, leaving behind the 

 structureless, filmy outer skin. The crystals were apparently 

 carbonate of lime, and their presence suggested that they 

 might be destined to furnish material for the shell of the 

 young snail before it broke loose from the Qgg. This sug-, 

 gestion was strengthened by examination of a number of 

 eggs just after the young snails, provided with a well-formed 

 spiral shell, had been hatched out. In all cases the thick 

 opaque coating of crystals was found to have disappeared 

 from the outer envelope of the egg, leaving behind a filmy 

 skin, dotted here and there with scattered crystals. Many of 

 the still sharp-edged crystals were found embedded in the 

 remnants of the albumen carried off by the young snail 

 attached to its foot, many more were seen lying inside of 

 the snail-shell against the animal's body, and a stiU larger 

 number, much reduced in size and with blunt or rounded 

 edges, appeared in both positions. Intermediate steps in 

 this process of translation of the crystals from the outer 

 coating of the egg could be traced on examination of juveniles 

 towards the end of the incubation period, so that the process 

 progressed pari passu with the later stages of growth of the 

 young snail-shell. Treated with dilute nitric acid, these 

 young shells gave a brisk effervescence, while the enclosed 

 animal similarly treated gave no reaction. 



At this stage of the inquiry a more diligent search through 

 the scattered literature of the subject showed me that a 



