BARBADOS-ANTIGUA REPORTS 59 
Circulatory System. In the abdominal region there is no dorsal vessel. 
One specimen had a dark line visible externally in the mid-dorsal region 
extending more than half way back, but investigation revealed no vessel. 
At any rate the muscular layer is too thick to permit such a vessel to be 
seen externally. The dark line was apparently due to a concentrated 
plexus of small vessels in the circular muscle layer. Other specimens do 
not show it. The chlorogogen masses of the intestinal region support a 
rich circum-intestinal plexus, that no doubt takes over the function of a 
dorsal vessel. (Plate VI, Fig. 1). There is a very conspicuous ventral 
blood vessel (Plate VI, Figs. 1 and 2) suspended by a longitudinal 
mesentery; circular vessels are present. In the thorax (Plate VIII, Fig. 
1) a dorsal vessel is developed, and the five anterior metameres contain 
each a pair of large, thick-walled ‘‘hearts.’’ (Plate VIII, Fig. 1). 
Whether these connect with a ventral vessel was not determined. The 
sixth and seventh thoracic segments have no ‘‘hearts,’’ but the septa 
are very vascular. This vascular condition of the septa is also found in 
the anterior abdominal metameres, and one specimen showed a large sinus 
filled with blood so located as to simulate a ‘‘heart.’’ 
Nervous System. The ventral nerve cord is of the ladder type, (Plate 
VIII, Fig. 2). There are no discernible gangliar enlargements. Directly 
above each hemisphere of the cord is a large hollow vessel (Giant fiber?). 
This hollow vessel is also found in the brain, which is located in the ex- 
treme anterior tip just above the mouth. (Plate V, Fig. 1) The nerves 
of the cord are large and regular, extending out at right angles. 
Excretory System. The ecelome in the thoracic region is filled with 
gray, glandular tissue, taking the form of much lobulated sacs. Whether 
these form one or several nephridia is not clear. They fill the cavity of 
each metamere; and a portion extends forward into the head, where the 
two sides unite into a common external opening just above the brain. 
(Plate) V, Fig. 1). Whether or not there are nephridia in the abdomen 
it is difficult to determine. 
Reproductive System. Not identified. Probably consists of gonads that 
are inconspicuous except in the breeding time. ; 
The Tube 
The tube is made from a secretion from the ventral shield glands. This 
secretion serves to stick together fine particles of mud so as to form a 
cylindrical tube, which is lined internally by the hardened mucus. As the 
animal grows, the tube is lengthened by building on at the anterior end. 
The animal revolves in the tube, while the pinne of the branchial filaments 
collect the particles of mud. The animal, rising partly out of the tube, 
uses the collar lobes as trowels which beat down the thin edge as they 
fold and clasp over the margin. The longest tube collected measures 
190 mm. 
When the animal is undisturbed, the branchie always protrude from 
the tube. At night they are only partially extended from the tube, 
though not expanded as during the day. Hundreds of specimens of this 
