A new species of Nectonemertes. 351 



Montgomery) are the most abundant and are speciall}' numerous 

 on the anterior, lateral and dorsal surfaces of the brain, but prac- 

 tically at all points form a sheath about the inner fibrous core, and 

 to some extent separate the dorsal and ventral lobes. 



The medium sized cells of Bürger (type II, Montgomery) are 

 said by these two authors to be confined to the ventral brain lobes 

 and tlie lateral cords, and we have satisfied ourselves that such is 

 the case in several species of nemerteans from the California coast. 

 In the present species however this type of cell is by no means 

 sharply defined. There are small numbers of nuclei, located about 

 the periphery of the fibrous core, which are slightly larger and are 

 imbedded in cytoplasm somewhat more abundant and spongy than 

 in the cells of the first type, but they blend so imperceptibly with 

 the small cells of Bürger that it is by no means certain they 

 represent a distinct class. Furthermore in the dorsal lobes elements 

 of essentially the same character appear, holding position chiefly on 

 the dorsal surface. Also in the lateral cords they exist in small 

 numbers. 



On the other hand several cells, which probably correspond to 

 Burger's large sized cells (type III, Montgomery), are present in 

 both the dorsal and ventral brain lobes, especially along their anterior, 

 ventral and inner surfaces; and they appear here and there in the 

 lateral cords. They contain round, clearly defined nuclei each with 

 a distinct nucleolus and uniformly distributed chromatin. 



The colossal neurochord cells, stated by Bürger and several 

 other authors to hold positions on the median surface of the ventral 

 brain lobes, may be readily discovered in some of the nemerteans 

 from the west coast of the United States but we have never been 

 able to detect their presence in N. peJagiea. 



In a cross section of the lateral cords, represented in Fig. 5, 

 13, 1(3, it will be seen that the fibrous portion forms two distinct 

 bundles, which with the surrounding nerve cells is enclosed in a 

 connective tissue sheath. Of these two portions the ventral has 

 fully three times the area of the dorsal, and when treated with 

 Delaeield's haematoxylin it presents a darker more compact 

 appearance. Furthermore in its fibrous portion numerous interlacing 

 fibres appear, while in the dorsal section the fibrils are uniformly 

 of small size and longitudinally parallel. Anteriorly this dorsal part 

 of the lateral cords connects with the dorsal brain lobe, while the 

 ventral portion is attached to the ventral half of the brain. Both 



