168 BULLETIN OF THE 
ocelli, each of a reddish color. Two of these are placed near the median line, 
and two appear near the bases of appendages called cephalic tentacles (f), 
Both pairs are situated in the dorsal walls of the head. In the cephalic walls 
below the median eye-spots there is a greenish spot of triangular shape. Sim- 
ilarly colored spots are also situated in the dorsal walls of the head under the 
lateral eyes. 
Two pairs of appendages, known as the cephalic tentacles (¢) and the cepha- 
lic setae (s), arise from the head. Both of these cephalic appendages are em- 
bryonic. 
The tentacles (f) are long, flexible bodies, which are sometimes closely 
coiled about their bases, and at other times widely extended. These append- 
ages are transparent, of a slightly reddish color, and unjointed. Their surface 
is covered with short stiff spines or hairs, which are especially numerous near 
their distal extremities. Each appendage has a cavity throughout its length, 
opening into the body cavity, and through the walls the circulation of a fluid 
contained within can be easily seen. There‘are two of these cephalic tentacles, 
both of which arise from the dorsal region of the head, a little above the lateral 
lines of the body, They are probably homologous to dorsal cirri. 
The cephalic sete (s) are smooth, easily deciduous spines projecting from 
ear-like lappets on the dorsal side of the head below the cephalic tentacles, 
Their length varies, but in young specimens it is about one half that of the 
body. Although generally carried separated in a fan-like manner, they are 
often folded closely together, parallel with the sides of the body (Fig. 6). 
The cephalic sete are probably homologous with the embryonic spines of 
(Nerine) Spio, and may be regarded as the sete of a single segment of which 
the head is formed. It is a significant fact that these spines, as far as known, 
are only found in those annelid larve which are free swimming. In the 
young Arenicola, for instance, which passes its youth enveloped in a mass of 
slime, these embryonic spines never appear. This fact leads one to ask if they 
are not special organs for defence rather than ancestral features descended 
from fossil forms, which according to A. Agassiz they sometimes closely re- 
semble. Their peculiar positions when a Nerine or Prionospio larva is alarmed 
leave no doubt of their defensive function. 
The mouth is terminal and slightly ventral. The proboscis is short when 
retracted, not extending back of the posterior part of the head. It is protru- 
sile even in this early condition, and bears a chetinous (?) toothed body of 
red color, visible through the mouth opening. The position of the posterior 
extremity of the proboscis is marked by a pair of diverticula (g) from the 
intestinal tract, whose walls are here pigmented with brown and yellow. They 
lie near the medial dorsal line, one on each side of the junction of proboscis 
and esophagus. These “glands” begin to form as small lateral diverticula 
from the cesophagus, and extend forward in the body cavity, one on each 
side of the proboscis. Later in their growth yellow pigment appears in 
their walls, and they assume a superficial likeness to glands. In the dorsal 
medial line, upon the intestinal tract between them, there is a pulsatile sac 
