LARVAL FORMS : THEIR NATURE, ORIGIN AND AFFINITIES. 889 
To the above characters may be added a glass-like trans- 
parency ; and the presence of a widish space, often traversed 
by contractile cells, between the alimentary tract and the 
body wall. 
Considering the very profound differences which exist 
between many of these larvse it may seem that the characters 
just enumerated are hardly sufficient to justify my grouping 
of them together. It is, however, to be borne in mind that 
my grounds for doing so depend quite as much upon the fact 
Fig. 5. — Larva of CephalopTiorous Mollnsca in the veliger stage. (From 
Gegenbaur.) A. and B. Earlier and later stage of Gasteropod. 
C. Pteropod (Cymbulia). v. velum ; c. shell; p. foot ; op. operculum; 
tentacle. 
that they constitute a series without any great breaks in it, 
as upon the existence of characters common to the whole of 
them. It is also worth noting that most of the characters 
B 
C 
c 
Fig. G. — Larva of Argiope. (From Gegenbaur, after Kowalevsky.) 
m. mantle ; b, seta; ; d. archentcron. 
