104 GASTROPODA. 



leathery consistency, are fastened to a similarly constituted, structure- 

 less membrane which, in its turn, is attached to a stone. The same 

 is the case with the capsules of Fasciolaria tulipa, in which the edges 

 of the cup are continued into a wavy membrane. The form of this 

 latter capsule seems to come nearest that of the well-known Janthina, 

 the cup-like capsules of which are attached to a kind of raft by 

 means of which the animal floats in the sea. This float is a large 

 spindle-shaped body formed of the same substance as the capsules 

 and containing air-spaces. It is connected by its pointed end with 

 the foot of the animal and from its lower side the capsules hang. 

 The float is also found in the male, and without its aid the animal 

 cannot move about freely in the water, so that it must not be 

 regarded merely as an organ connected with oviposition, although it 

 may perhaps be considered to have been primarily developed for this 

 purpose. 



The conditions of oviposition in the terrestrial Gastropoda differ 

 somewhat from those of the aquatic forms. The eggs of the for- 

 mer may also be surrounded bv a gelatinous albuminous substance 

 and may be connected together into spawn-masses which resemble 

 rows of beads (Lima.' 1 ) or else may be massed in larger numbers to 

 form gelatinous balls {Onchidium). In the latter case, the structure 

 of the spawn is rather more complicated, each egg being surrounded 

 by a mass of albumen which is enclosed in a transparent but resist- 

 ant envelope. The latter lengthens in a line with the two opposite 

 poles of the oval albuminous mass, forming at each end a thread 

 winch is continued into the envelope of another egg, so that the 

 eggs constituting the spawn are connected into wreath like chains 

 which are again surrounded by the common gelatinous mass. The 

 albuminous mass surrounding the egg usually, in the terrestrial 

 Gastropoda, becomes still further protected by a firm membrane 

 impregnated by lime-salts. A more or less thick calcareous shell 

 is thus formed around the egg : this, even in Helix [xmiatia, is of 

 somewhat firm consistency. The eggs are usually deposited in great 

 numbers (60 to 80 in Helix pomatia) in small holes in the ground pre- 

 pared by the parent animal and are then covered over with earth. 

 Species of BuUmus which live on trees roll up leaves into the form 

 of cornucopia' and lay in these their soft-shelled eggs. 



The eggs of the terrestrial Pulmouata attain a considerable size. 

 Even the eggs of Helix pmivitia measure 6 mm. in diameter. Those of 

 the Ceylon form, Helix (Aoivtttt) Waltoid are as large as a sparrow's 

 egg (P. and F. Sakasix. No. 102), and those of an American species 



