426 THE AMERICAN NATURALIST. (Vor: XXXIX. 
25 meters in length when fully extended, but remains as slender 
as a thread; still another (Cerebratulus lacteus) grows to be 7 
meters long and 20 mm. wide, while the single known individual 
of Euborlasia maxima was 45 mm. in width after preservation. 
Although the body is without external segmentation, many of 
the internal organs are metamerical arranged. The body is 
covered throughout with glandular and ciliated epithelium. A 
true body cavity being wanting, the space between the muscular 
walls of the body and the intestine is filled with gelatinous 
tissue, or parenchyma. Many species of the Heteronemertea 
have a delicate caudal cirrus beneath the anal opening at the 
posterior end of the body, and the representatives of a single 
genus (Nectonemertes) are provided with a pair of lateral swim- 
ming appendages near the anterior end of the body. 
The proboscis is bathed in a corpusculated fluid, enclosed in a 
Special muscular sheath, and opens at the anterior end of the 
body, sometimes in connection with the mouth and sometimes 
separately. In many species it is nearly as long as the body 
itself; it is lined with glandular epithelium, and in certain genera 
is provided with rhabdites or nematocysts. In one of the four 
orders (Hoplonemertea) there are highly specialized calcareous 
stylets of such definite size and shape that they form most con- 
venient and reliable diagnostic features. 
The mouth is situated anteriorly, either in front of the brain, 
as in the Hoplonemertea, or immediately behind it, as in the 
other two orders. The mouth leads into the esophagus, which 
is often demarcated from the succeeding portion, the stomach ; 
the latter opens into the intestine, which in most genera is pro- 
vided with paired lateral diverticula. In the Hoplonemertea the 
stomach is prolonged into a narrow tube, pylorus, which opens 
well back of the anterior end of the intestine, the latter thus 
extending forward beneath the pylorus as the intestinal caecum. 
Other appendages occur in certain species. 
The blood circulates in two or three longitudinal vessels, which 
usually have numerous anastomoses and open into one or more 
large lacunz in the head. 
The excretory organs, or nephridia, usually consist of a pair 
of lateral canals, the ramifications of which lie in close relation 
