POST-LARVAL STAGE OF ARENICOLA MARINA. 49 
“The two extremities of the body were in each of the larve 
yellow. This yellow colour was due to a number of yellow bodies 
or cells apparently situated in the epidermis. The blood was dis- 
tinctly reddish.” 
“The gelatinous tube seemed to invest the body closely, and was 
certainly no impediment to the animal.” 
These two specimens are practically identical. 
The worm is about 6°8 millimetres in length. It consists of a 
prostomium, without eye-spots, but with a light area or depression on 
each side in which is lodged the otocyst, followed by a peristomium 
and twenty cheetigerous somites forming the anterior region, with a 
tail of a greater number of somites—some thirty or more—terminating 
in a small pygidium or anal somite. 
These tail somites are difficult to enumerate, as the septa are not 
well developed, but each segment is surrounded by a band of gland- 
cells, which serve for their demarcation. 
The worm is surrounded by a structureless gelatinous-looking enve- 
lope or tube (figs. 1, 4), probably secreted by these gland-cells, which 
are not confined to the tail, but occur in every somite ; in fact, they 
are more abundant in the anterior somites, and here occur in two 
bands per somite, separated by a narrow non-glandular band (see 
fig. 7). This closely investing gelatinous tube seems, when taken in 
connection with sundry internal arrangements, such as nephridia, 
septa, &c., to point to an affinity with the Chlorhemide. 
As will be seen from the accompanying figures (fig. 1), the dorsal 
bundle contains two long capillary cheetee, of which one is longer than 
the other. 
The peristomium is achzetous ; the first dorsal bundle is represented 
by a minute dorsal cheta (Ch. 2), scarcely protruding from the body, 
in Somite 2. At first sight the entire region between the pro- 
stomium and the first long cheta appears to be achetous, but this 
region is divided into two portions by a slight groove ventrally, and 
careful observations showed this small cheeta (Ch. 2, fig. 1), demon- 
strating the composition of this region. In the adult Arenicola the 
achetous region following the prostomium has been regarded on 
other grounds—to wit, the existence of two septa anterior to the 
first bundle of chetee—as being composed of two somites. 
This small cheta, then, probably disappears in the adult, as has 
been shown to be the case with the anterior chetz in some other 
Polychetes. : 
The ventral chete commence in Somite 3; they are much 
shorter than the capillary cheetz, being only about twice the length of 
the thickness of the body-wall. Hach cheta is a sigmoid hook, with 
a small but distinct notch (fig. 2), the lower prong being the larger. 
NEW SERIES.—VOL. III, NO. I. 4 
