NEMERTEANS I47 



mously developed as far posteriorly as the anterior portion of the intes- 

 tinal region. In few other Iloplonemcrteans is the proboscis sheath 

 so powerful as in the present species (p1. xviii, fig. i). 



Ocelli. — The snout when well extended is sharply pointed, but can 

 be withdrawn to a considerable extent into the tissues of the head. 

 For this reason the two very small ocelli which are situated near the 

 tip of the snout (p1. xxi, fig. i) are likely to be overlooked, and are 

 difficult to see in the living worm. They lie deep in the tissues of the 

 head and can usually be seen clearly only after the specimen has been 

 cleared in cedar oil or some other suitable medium. Sometimes instead 

 of two single ocelli, we find two groups each made up of two or more 

 minute pigment spots (p1. xxi, fig. 2). 



Cerebral Sense Organs. — These are extremely small, measuring 

 scarcely more than one-tenth the diameter of head in same region, lie 

 some distance in front of brain, and connect with exterior on latero- 

 ventral margin of head near tip of snout. 



Cephalic glaitds are voluminous, composing the greater portion of 

 the tissues of the head in front of brain. They are much interspersed 

 with connective tissue and muscle fibers, and do not extend posteriorly 

 to the brain in any considerable numbers. There are a few isolated 

 submuscular glands in the esophageal region. 



Brain small as compared with the diameter of head, but of the 

 usual proportions. 



Muscular System. — Just in front of brain, and in the region of the 

 attachment of proboscis to its sheath, a longitudinal muscular layer 

 arises quite independently and is distinct from the longitudinal muscles 

 of the body walls. These muscles surround the brain, esophagus, and 

 proboscis sheath. This secondary longitudinal muscular layer in- 

 creases greatly in size back of brain, but remains separated from the 

 musculature of the body walls by a thick layer of parenchyma. Back 

 of the brain this muscular layer (/;;/', p1. xviii, fig. i) becomes thicker 

 than the main longitvidinal layer (/?«) of the body walls, and its fibers 

 are larger, more closely placed in their bundles and stain more deeply. 

 It reaches a considerable distance into the esophageal region, but gradu- 

 ally the bundles comprising it become more and more separated from 

 each other by parenchymatous tissue, and gradually they approach 

 nearer the body walls. Some of the fibers attach themselves to the 

 proboscis sheath just outside the circular muscular layer. Eventually 

 they become arranged just internal to the longitudinal muscles of body 

 walls and form a portion of this layer. Their fibers are much larger, 

 however, and by an increase in number farther back give rise to the 



