278 
J. STEPHENSON. 
without the intervention of a peritoneal layer, do so in the 
younger stages almost over the whole surface of the mass. 
In other words, the chromophil cells are not derived from a 
previously differentiated flattened peritoneal layer ; the 
chromophil cells, and the flattened peritoneal cells which 
cover neighbouring structures, are equally specializations of 
the lining cells of the coelomic cavity. The inference, drawn 
from the appearances in the smaller masses of cells in 
Helodrilus parvus, that the chromophil cells are derived 
from the peritoneum, requires to be understood in the above 
sense ; the often flattened cells of the peritoneal membrane, 
which in the adult covers the greater portion of the mass, 
are derived from the superficial cells of the chromophil 
tissue, with which (cf. the description of P. ha way ana) 
they may still be connected, rather than vice-versa. 
Young Helodrilus Parvus. — Two small specimens, in 
diameter ‘7 mm. in the anterior part of the body, were 
examined; and several still smaller, *5 mm. in diameter; 
even in some of these small specimens sexual organs, both testes 
and ovaries, were beginning to form. Since the appearances 
are merely, for the most part, confirmatory of what has gone 
before, a short account will be sufficient. 
The chromophil cells scarcely penetrate at all into the 
muscular felt on the dorsum of the pharynx, and form only 
the lobed masses round the muscular strands which emerge. 
In the larger of these specimens these lobes extend back- 
wards through segments Y and YI ; smaller patches of the 
cells are present in VII, VIII, and IX on the walls of some 
of the blood-vessels, on the septa, and in the angle between 
the septum and the alimentary tube ; a few cells form a 
flattish layer on the ventral vessel in segment X. In the 
smaller specimens the lobes extend backwards, segmentally 
arranged, as far as segment VIII ; they are as usual suspended 
on muscular strands passing obliquely to the parietes, and are 
also connected in a longitudinal series through the septa by 
thick strands of connective tissue, which, piercing the septa 
as cords, spread out somewhat in the lobed masses. The 
