SIANDEN : CAIX'ARKOUS ECCS OK rEKKKSTRI AI, MOLLUSCA. 155 



regular crystallisation is not so pronounced in other cases where the 

 Hme is deposited in grains, as in the eggs of birds, or the bones of 

 vertebrates. A certain amount of flexibility is absolutely necessary 

 in the large calcareous eggs of some species to allow of their passage 

 through the comparatively narrow aperture of the parent shell. A 

 case in point is that of Acai'us skinneri Rve., whose egg some time 

 after extrusion cannot be inserted into the shell from whence it came. 



The eggs of most of the naked snails or slugs are soft, semitrans- 

 parent, and destitute of calcareous crystals. The genus Ariou affords 

 a notable exception. The egg of Arion ater L. has a soft membran- 

 ous envelope when first laid, but this soon becomes opaque through 

 the deposition of immense numbers of minute calcareous particles on 

 the interior. The same thing occurs in the genus Cryptella, from the 

 Canary Isles, but, as in Arion, the crystals are ill-formed and exhibit 

 the rhomboidal figure very imperfectly. I may here remark that such 

 eggs as these cannot well be preserved in a dry state owing to shrink- 

 age, the amount of calcareous matter secreted being insufficient to 

 give the envelope the requisite stability. 



In form, the calcareous eggs of snails are, for the most part, oval, 

 elliptical, or spheroidal. None show the well defined " big and little 

 ends " observable in the eggs of many birds. The egg of Columna 

 flammea Martyn, from Principe Island, is ovate-oblong or kidney- 

 shaped, 14 mm. in length. 



The colour of calcareous eggs is usually white, in varying shades, 

 but in many of the AcJmtinidce it is a peculiar shade of yellow. In 

 Paryphanta hochstetteri Pfr. it is fulvous. Some eggs recently received 

 from Bombay are rose-pink, but as the shells to which they belong 

 are not yet to hand I cannot give the species. 



In size, the eggs of snails vary as much as the animals which pro- 

 duce them, but it does not necessarily follow that from a large shell 

 a proportionally large egg may be expected. Study of the apex — the 

 part formed within the egg, and known variously as the "protoconch,'' 

 " nucleus," " dome," or " nepionic whorls " of any shell gives us a 

 fairly accurate idea of the approximate size of the egg belonging 

 thereto, when the egg itself is not forthcoming for comparison. It is 

 to the large-domed species we must therefore turn for correspondingly 

 large eggs, in which the embryo undergoes a greater amount of deve- 

 lopment within the egg, which contains a considerable amount of 

 nutriment ; consequently the individual eggs are of large size and few 

 in number. 



The oviparous land snails generally care for their eggs by placing 

 them in situations where they will not only be safe from injury, but 

 also open to the influence of air and heat, and in close proximity to 



