ALASKA NEMERTEANS 13 



The epithelium of the body is very thick, and filled with closely 

 packed gland cells. The two circular muscular layers in the esopha- 

 gal region show almost no indication of a mutual crossing of fibers 

 either above or below, although, as indicated in pi. ix, fig. 3, a few 

 fibers of connective tissue and fine nerve fibers pass at intervals 

 from the region of the median dorsal nerve to the internal circular 

 muscles. 



Proboscis. Attached to tissues of head just opposite the mouth, 

 and therefore a considerable distance back of the brain commisures. 

 Its posterior attachment is in the region of the efferent nephridial ducts. 

 The muscular layers are as in other species of the genus. Two large 

 nerves enter the latero-ventral portion of the proboscis at its attach- 

 ment, and pass backwards on opposite sides just internal to the cir- 

 cular muscular layer. 



The proboscis sheath shows a homogeneous basement layer beneath 

 its internal lining of flattened epithelium. The musculature consists 

 wholly of circular fibers, except that there is a distinct layer of longi- 

 tudinal muscles between the circular muscles of the proboscis sheath 

 and the epithelium of the esophagus. Lying on the muscles of the 

 proboscis sheath is a small median dorsal nerve which runs parallel 

 with the median nerve outside the circular body-muscles and corre- 

 sponds to the inner median nerve of other species. 



The esophagus is provided with a pair of nerves continuous with 

 the unusually large buccal nerves. The cerebral ganglia are situated 

 wide apart, as in other species. The anterior portion of the head 

 receives a considerable number of remarkably large nerves (pi. ix, 



% i). 



Cerebral sense organs. These organs deserve special attention 

 because of their high degree of development. They are each pro- 

 vided with a narrow but distinct canal leading outward to the lateral 

 surface of the integument. The sense organs lie immediately external 

 to the dorsal ganglia, from which they are separated only by a few 

 fibers of connective tissue which here represent the integumental base- 

 ment membrane (pi. x, fig. 2). In size, position and structure these 

 organs are closely similar to those of C. annulata, as figured by 

 Burger. 1 Each consists of a large, rounded mass of nerve cells and 

 connective tissue surrounding a narrow, central canal lined with 

 ciliated and specialized sensory epithelium (pi. ix, fig. 2). Periph- 

 erally there is an abundance of peculiar glandular cells, and the 

 whole is separated from the surrounding integumental cells by a thin 



1 Fauna und Flora des Golfes von Neapel, Monogr. 22, pi. xn, fig. 5. 



