F. M. Turnhidl — Anatomy and Hahits of Nereis virens. 267 



The mules are easily distinguished from the females by ditferences 

 in color and in the form of the side appendages. The color of the 

 body in the male is an intense steel-blue, which blends into green at 

 the base of the lateral appendages. These have a rich and brilliant 

 sea-green color which is heightened by the complimentary effect of 

 the luimerous red blood-vessels they contain. The latter are especially 

 noticeable toward the posterior end of the body where the skin is 

 thinner and less opaque, so that the appendages, with their network 

 of ca|»illaries, appear bright red. 



In the female the body is of a dull greenish color, with a slight tinge 

 of orange and red. The appendages are orange-green at the base, 

 and become bright orange toward their extremities ; but sometimes 

 they are greenish throughout. The whole surface of the skin, in both 

 male and female, is iridescent, reflecting bright hues when placed in 

 the light. 



The head (figs. 1 and 15, a) is small, and flattened on the doisal and 

 ventral sides. From the position of the anterior eyes the sides taper 

 toward the anterior extremity, where it is rounded oft' and terminated 

 by a pair of small antenna (figs. 1 and 15, h, b). There are two pairs 

 of eyes on the upper surface of the head, one pair near its base and 

 another pair more anterior and farther apart. The anterior eyes are 

 situated near the middle and on the broadest portion of the head. 

 On each side of the head, attached to its anterior half and also to the 

 buccal ring, is a large antenna or palpus, as it is sometimes called (figs. 

 1 and 15, c). These are stout, fleshy and somewhat contractile organs. 

 Each has a small rounded lobe at the tip (figs. 1 and 15, c'). 



The buccal segment and the head constitute the cephalic or head 

 region. The tegument about the mouth is wrinkled and folded lon- 

 gitudinally, presenting an appearance like the mouth of a purse, when 

 drawn together by strings. The tentacular cirri are long, slender 

 and quite flexible. They receive their nerves from the first abdominal 

 nerve-ganglion, whereas the antennae receive theirs from the head- 

 ganglion. 



There are four pairs of tentacular cirri, two dorsal (fig. 1 , ee, ee') and 

 two ventral (fig. 1, e, e'). The ventral ones are situated nearer to the 

 palpi than the doi'sal, and hence the two are called respectively the 

 internal and external tentacular cirri. The relative lengths of the ten- 

 tacular cirri are shown in fig. 1. The two large dorsal tentacular cirri 

 (ee, ee) are longer in the male than in the female. In the male they 

 will reach to about the middle of the ninth segment, when laid along 

 the back. In the female they will reach to about the middle of the 



