NIERSTRASSIA FRAGILE. 237 



homogeneous substance which extends between the cells far down toward their 

 bases. The origin of this substance could not be determined. Neglecting 

 differences in size these types of cells form the epithelial lining as far as the 

 opening into the stomach-intestine. 



As far back as the stomach-intestine, the digestive tract is surrounded by 

 a layer of circular muscles among which numerous radial strands occur, extend- 

 ing to the body wall. Among these elements, from the anterior end of the 

 animal to a point a short distance behind the brain, numerous solitary, pyi'i- 

 form gland cells occur and open by intercellular pores into the digestive tract. 

 In some instances the secretion is abundant, the small spherical granules staining 

 intensely, but especially behind the brain the granules become relatively smaller 

 in size and amount, vacuoles occupying a considerable portion of the cell. 



A radula, of the distichous type, is present, and so far as may be determined 

 from sections comprises 15 rows. The form of each tooth is represented in 

 Plate 2, fig. 10, while the radula sac and odontoblasts are faintly shown in 

 Plate 6, fig. 3. In this last figure a small ridge, composed of slender cells, occupies 

 the position of the subradular organ, but while it presents the appearance of a 

 sensory area no definite gangUa have been found in connection with it. 



Paired ventral saUvary glands are present in the form of small, globular 

 sacs (Plate 6, fig. 3) that on one side at least develop small lobes. One of these 

 is unusually swollen in the longitudinal section and appears to contain a few 

 parasites. The cells are relatively small, vacuolated and in some instances 

 contain a finely granular secretion. 



The stomach-intestine exhibits the usual sacculated form and relations 

 to other organs; and the glandular epitheHum is not essentially different from 

 that of other neomenians. In the longitudinal sections large numbers of some 

 parasitic protozoan are present in various stages of development and may be 

 responsible for the unusual size of some of the epithelial cells. Posteriorly the 

 canal narrows, becomes laterally compressed as it passes between the limbs of 

 the shell gland and then in the form of a very slender canal makes its exit into 

 the cloacal chamber. As these animals came in unattached with no food in the 

 digestive tract there is nothing to indicate the nature of their habitat. 



Owing to the abundance of connective tissue in the visceral cavity it is 

 very difficult to accurately trace the course of the blood, but in its main features 

 the circulatory system is typical. The heart, much contracted, is a tubular 

 structure (Plate 6, fig. 5) in two divisions possibly separated by a valve though 

 this was not clearly demonstrated, and throughout much of its extent it is free 



