Snail-Leeches. 85 



At the time when the Glossiphon is ready to deposit her eggs 

 she may be observed to be very uneasy, twisting herself about 

 in a peculiar manner, and contracting her body violently into 

 one position ; by and by a thin jelly-like secretion encircles 

 that portion of the body from which the vitelli come out; 

 simultaneously with the formation of this surrounding belt of 

 jelly, the vitelli are excluded in small masses at a time ; they 

 are thus contained within this secretion, and the animal, by a 

 particular twist of the body, extricates its head and neck from 

 the gelatinous belt, which, with its contained vitelli, now forms 

 an egg and adheres to the side of the glass. After an irregular 

 lapse of time the same performance will be again gone through, 

 and a second egg, or batch of vitelli, will be deposited, and a 

 third, or fourth, etc., at intervals. If the reader will refer to 

 what I have said (Intellectual Observer, No. xi., 1862, 

 p. 357) on the subject of the Nephelis engaged in laying her 

 eggs, he will be able to compare the one phenomenon with the 

 other. A viscid secretion, which ultimately forms the vitelline 

 membrane, or egg covering,* occurs both in Nephelis and 

 Olossiphonia ; the vitelli are inclosed after the same manner 

 within this secretion, and both animals extricate themselves 

 from the surrounding belt pretty much in the same manner. 

 But the secretion, which in both forms a vitelline membrane,t 

 remains in Qlossiphonia unchanged; it is a thin gelatinous 

 fluid, adhering by a pedicle to the substance to which it is 

 attached; while in Nephelis the secretion undergoes consider- 

 able change, instead of retaining the consistency of thin jelly, 

 it gradually alters, at first assuming a firmer character, and at 

 length, after the lapse of a few days, becoming quite leather- 

 like in its nature. 



The Nephelis, it will be remembered, uses its mouth, and 

 fixes the egg (capsule and vitelli) to some object; but the Glossi- 

 phon appears to press its ova to the sides of the glass by the abdo- 

 men. After all the eggs are laid, the Glossiphon — those species, 

 that is, which exhibit this habit — settles down to a quiet 

 domestic life, continuing at home, and nursing her embryo fry. 

 The changes in each vitellus may be readily noted each 

 day, the process of segmentation marked, and the gradual 

 development into a young and perfect Glossiphon watched with 

 delight and instruction. The usual time which a snail-leech 

 occupies in her incubating task is about ten days, but it may be 

 longer or shorter ; the embryo drop out of the vitelline mem- 



* This Tiscid pellucid membrane represents the chorion; the round grains, 

 which are about the size of a large pin's head, are the vitelli ; both together 

 forming an ovum. 



t Dr. Johnson is in error when he states that the vitelli of the snail-leeches are 

 not inclosed in a capsule, which, however, from its transparency, is not readily 

 discernible. 



