552 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
Lineus bilineatus McIntosh. Northern coasts of Europe, Medi¬ 
terranean, Madeira. Chaupius (’86) describes a specimen which 
contained embryos, although other observations indicate that the 
species usually deposits its eggs. 
Besides these forms, which are supposed to be strictly vivip¬ 
arous, several other species may have the eggs fertilized while 
within the body of the parent. This is the case in Carcinonemertes, 
in certain species of the fresh-water Stichostemma, and in Geone- 
mertes australiensis. 
In Carcinonemertes and some species of Stichostemma the egg 
may proceed in its development as far as the early stages of cleavage 
before being deposited. Indeed, in Carcinonemertes carcinophila , 
although most of the eggs of an individual are deposited immedi¬ 
ately after fertilization and before cleavage, yet a small proportion 
of them may be retained in the body until the later stages of 
cleavage or even until the formation of free-swimming embryos 
(Coje, : 02). In these forms, then, we find a striking intergradation 
between the strictly oviparous species and the few forms which are 
known to be regularly viviparous. 
It seems conceivable, therefore, that Geonemertes agricola , which 
may be considered as normally viviparous, may under certain circum¬ 
stances actually discharge its eggs while they are still in the early 
stages of development or even before cleavage, and that such eggs, 
deposited either in damp earth or in sea water, are fully capable of 
complete development. 
Copulation. — In a normally viviparous animal in which the eggs 
do not develop parthenogenetically, some form of copulation is to be 
supposed. Nevertheless, Child (: 01, p. 998) finds in Stichostemma 
that both kinds of sexual products mature in the same gonad at the 
same time and are discharged together; hence he believes that self 
fertilization usually occurs. Among the viviparous nemerteans sev¬ 
eral species have been observed in the act of pairing, an act which 
from the nature of the worm, with its hundreds of pairs of sexual 
openings along the sides of the body, must of necessity be a very 
simple process. 
In Carcinonemertes a number of writers have observed the male 
and female worms to place their bodies side by side, either in an 
outstretched condition or somewhat folded, and then to secrete a 
large amount of mucus which encloses the bodies of both worms in 
