GASTEROPODES. 281 
in general. When adhering to the surface of the vessels whereon speci- 
mens repose, it should be removed. The Abbé Dicquemare remarks, 
that an organ beneath the posterior extremity is the source of this 
mucous matter. 
Some of the race of the Doris are more languid than others, but all 
are extremely sluggish. The smaller swim supine, but they can be 
seldom incited to motion. 
From the great diversity of size and colour, from the scantiness of 
the branchie, their dimensions and appearance, also from the indentations 
of the flap, sometimes seeming an entire piece, sometimes cleft almost in 
two down the middle, I was long induced to contemplate the subdivision 
of the Tritonia Hombergii into distinct species. But after seemg many 
of all different dimensions, colours, and proportion, extending between 
four lines and eight inches, I am not prepared to deny the identity of 
the whole as belonging to a single species. Progressive evolution pro- 
duces an incredible change. 
Pirate XX XVIII. 
Fic. 1. Tritonia [Doris] Hombergii, adult, back. 
2. Belly. 
. Corniculum of an adult. 
. Branchie. 
. Younger specimen with few branchiz, back. 
. The same, profile. 
. Corniculum of the same, enlarged. 
. One of the branchiz of the same, enlarged. 
. Minute specimen. 
. The same, enlarged. 
. Spawn of fig. 5. 
OS CTH on SP 
a 
ic 
. Portion of spawn, enlarged. 
. Another deposit of spawn. 
. Nautiline from the spawn, magnified. 
. Nautiline from the spawn, magnified. 
. Nautiline from the spawn, magnified. 
17. Nautiline from the spawn, magnified. 
18. Empty shells of the Nautiline, enlarged. 
ee 
GS Ot em OF bP 
2N 
