368 ANDROGYNOUS MOLLUSCA. 



which are large, strung together like a necklace by a narrow 

 thread. Swammerdam has noticed the peculiarity in other 

 species. " Some snails," he says, " lay their eggs up and 

 down on the ground, others tie them all together like a 

 chain." The form of the egg is spherical or oval ; and their 

 colour is usually bluish-white or milk-white unstained by any 

 markings. The eggs, however, of the Helix bicarinata and 

 H. purpurea are of a beautiful yellow, a colour which also 

 distinguishes those of the Agathinae indigenous to Africa 

 and its islands.* In size the ova vary as much as do the 

 creatures from which they come : in the common snail 

 (Helix nemoralis) they are not larger than mustard-seed, 

 and their necessary minuteness in such a diminutive Mollusk 

 as Helix pygmaea must render them invisible to our eye ; 

 but those of the Bulimus haemastomus, Lamk. are almost as 

 large as a pigeon's, and with a shell equally hard and calca- 

 reous, f The arboreal species of Bulimus which inhabit the 

 Philippines " deposit their eggs in little clusters on the 

 trees, between two leaves which the animal manages to curl 

 up, one upon the other, so as to form a receptacle for their 

 protection; and so far as Mr. Cuming's observations go, 

 they are all soft, like snake's eggs, with the single exception 

 of the B. mindoroensis, in which instance the eggs are calca- 

 reous, deposited upon a leaf in parallel rows, each standing 

 perpendicularly on end, attached at the base by a glutinous 

 substance." J The earthborn tribes exhibit less or no arti- 

 fice, beyond that little which leads them to conceal their 

 fruit in a sort of subterranean nest, or lay them under stones 

 or clods of earth, or hide them in moss or amidst decaying 

 leaves, where they hatch secure from the evil influence of 

 the sun and of the summer's drought. 



Being laid, the eggs even of the land Mollusks rapidly 

 acquire an increase of size, for the volume of the entire 

 mass, deposited in the space of from twenty-four to thirty- 

 six hours, almost always exceeds that of the animal even 

 with its shell included. And the external envelope or shell 

 acquires also additional opacity and hardness, which proceeds 

 from the gradual and successive deposition of a great quan- 

 tity of particles of carbonate of lime over its whole inner 



* Ann. des Sc. Nat. xxiv. p. 25, 37. 



t See also Encyclop. Method, i. 319. Lister has figured the egg. Hist. 

 Conch, tab. 23, fig. 21. The egg of Voluta hrasiliana has a diameter of 

 seventy millim. while the animal itself has only two hundred. Ray Rep. 

 on Zoology, fyc. 1845, p. 119. 



t L. Reeve in Ann. and Mag. N. Hist. ser. 2, i. 273. " The tropical 

 Bulimi cement leaves of trees together to form an artificial nest for their 

 large eggs." OWEN'S Lectures, 308. 



