BULLETIN 39, UNITED STATES NATIONAL MUSEUM. [10] 



they are only accessible by climbing or cutting down the trees. It is 

 said that Cuming, the celebrated collector in the Philippine Islands, 

 maintained a corps of several hundred natives constantly occupied in 

 cutting down trees for the purpose of obtaining the fine Selicidce, for 

 which the forests of that region are renowned. 



EGGS. 



Most terrestrial moUusks lay eggs which are covered with a pellucid 

 membrane, a white and leathery or even a solid calcareous shell, like 

 that of a tortoise egg. These eggs may be found in the haunts of the 

 moUtisks themselves, most commonly in cool, moist places. Those of 

 American Selicidce are usually white, translucent, and associated to- 

 gether, though not deposited in a mass. Biilimus lays eggs that usually 

 Iiave a calcareous shell. The B. ovatus of the Antilles has an egg-shell 

 half an inch in length, in which the youn g moUusk develops, emerging 

 with several whorls of its spire completely formed and differing from 

 the adult only in size. The amphibious Ampullaria lays its eggs on the 

 the stalks of plants growing in marshy places, to which they adhere by 

 an abundant secretion of a partly calcareous nature, which, when dry, 

 forms a brittle animal cement. In Stenogyra the eggs may be seen 

 through the translucent shell and aiDparently are only discharged when 

 ready to hatch. They are so nearly the full size of the caliber of the 

 whorl, that it is astonishing how they can, together with the soft parts, 

 be contained in it. The oviposition and biography of reproduction in 

 many species are entirely unknown. By careful and patient observa- 

 tion th<i collector has it in his power to add largely to the sum of our 

 knowledge in this particular. 



ENEMIES OF LAND SHELLS. 



As it is often advantageous for the collector to know the enemies of 

 the objects of his search, a word or two on that point may be in place 

 here. The chief enemies of land mollusks are birds and small mam- 

 mals, mice, shrews, etc. In JiTorth America the birds seem to pay less 

 attention to snails and slugs than do their analogues in Europe. Still 

 the thrushes, blackbirds, and some water birds make use of them for 

 food. A singular sausage-shaped parasite, of which one end is atten- 

 uated into a slender tube, is found in Succinea. The soft parts of snails 

 thus affected are much distorted. The parasite is one phase of a Dis- 

 toma or fluke- worm, and is of a dark brown color and over an inch in 

 length. It is known as Leucochloridium americanum Dall. An analo- 

 gous species has been described from French Succineas, which is of a 

 mottled green. This parasite attains its development in the intestines 

 of thrushes which feed on the Succinea, and may perhaps be fatal to 

 these birds. Smaller Distomas are found in certain species of Limncea, 

 and develop into the liver-fluke, so fatal to sheep. The mollusks are 

 eaten, with the grass upon which they rest, by the sheep, which also 

 €at in the same way large numbers of Helices in Britain, and are said 



