598 F. H. GRAVELY. 
(1) Protrochophore: An unsegmented larva in which the 
“ preoral ” ciliated band is represented by an extremely broad 
band of short cilia (text-fig. 1). 
(2) Trochophore: This differs from the last only in 
having the diffuse ciliated band replaced by a narrow band 
of long cilia. 
(3) Metatrochophore: The simplest form of segmented 
larva : 
(a) In the first metatrochophore stage no parapodia are 
present. 
(b) In the second metatrochophore stage parapodia appear, 
but do not fuvction as organs of locomotion. 
Txt-pre. 1. 
Protrochophore of a Eunicid (from Hacker, after Claparéde and 
Meeznikow). 
(4) Nectochzta: The preoral ciliated band is replaced 
as primary swimming apparatus by the parapodia with 
their sete. This is the definition given by Prof. Hacker, but 
it is usually extremely difficult to determine the period at 
which this change takes place. Even in the case of Polynoé, 
in which the larva continues its pelagic existence for a con- 
siderable time after the disappearance of the ciliated band, 
the more advanced pelagic larvee settle to the bottom when 
in captivity and use their parapodia for crawling only, those 
specimens in which the ciliated band is still present holding 
the parapodia motionless until movement by means of the cilia 
is impeded. The term has, therefore, come to be used some- 
