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 (t), 

 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 (t) and the cepha- 

 lic setaj (s), arise from the head. Both of these cephalic appendages are em- 

 bryonic. 



The tentacles (<) 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 setse (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 setae are probably homologous with the embryonic spines of 

 (^Nerine) Spio, and may be regarded as the setae 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 larvae 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 chaetinous (1) 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 j'ellow. They 

 lie near the medial dorsal line, one on each side of the junction of proboscis 

 and asophagus. These " glands " begin to form as small lateral diverticula 

 from the oesophagus, 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 siTperficial likeness to glands. In the dorsal 

 medial line, upon the intestinal tract between them, there is a pulsatile sac 



