GYMNOSOMATOUS PTEROPODA 399 
and indépendant in motion; it may be telescoped into the 
c\lindrical part immediately in front, and at such times the 
caudal part of the trunk is truncated. The body is every- 
where covered with vibratile cilia. 
Trichocyclus hansineènsis uses its fins far less than Clione 
kincaidi. Progressive movements of T, hansineènsis are 
efïected by the constant motion of the cilia, of the ciliated 
grooves, which are rather large; the general cilia of the 
body may also aid in this. The body is capable, with the 
head, to be contracted into a round sphere. Part of the body 
may be contracted while the rest is expanded, but complété 
extension of any part of the body is never efïected unless 
the whole body expands. During moderato expansion, from 
3 to 5 rings are présent in the région between the posterior 
and middle grooves. The color of T. hansineènsis is mostly 
due to the liver which i» red and practically fills the entire 
trunk up to the cylindrical posterior portion. The fin-stroke 
in T. hansineènsis is more rapid than in C. kincaidi: in an 
individual of ca. 6 mm., it was 160 per min., but then Tricho¬ 
cyclus may rest its fins for ca. 30 sec. The fin-stroke in 
T . hansineènsis varies also according to the size of the in¬ 
dividual. This variation is not so striking in C. kincaidi 
where it is more uniform irrespective of size. 
Boas (1886) and Pelseneer (1887) in their admirable works 
on Pteropoda, classify Trichocyclus as a larva of either Clione^ 
Clionopsis^ or Notohranchæa. Both authors agréé that the 
young of Clione are provided with three ciliated grooves. 
Boas daims that the ciliated grooves are sometimes retained 
until late in life but are often lost early. He observes : (1) 
« Eight specimens 9, 12, 13, 16, 21, mm. were devoid of 
ciliated grooves; (2) one 26 mm. had the posterior furrow; 
(3) one 27 mm. had part of the posterior furrow only; (4) 
one 14 Va mm. lacked the middle furrow but the posterior 
and parts of the anterior furrows were présent; (5) one 
14 mm. had all grooves présent hut only part of the middle; 
(6) one 15 mm. had ail grooves présent, the middle being 
defective; (7) one 12 mm. had ail three ciliated grooves, and 
also one 16 mm. specimen had ail of them. » 
