244 



The Philippine Journal of Science 



1913 



gravel. Thalassema sorbillans was found in the top layer of 

 sand, more than 100 specimens being collected in a space 1 meter 

 square. I was able to keep a number of individuals alive in an 

 aquarium for several days, but was so busy with other work that 

 I did not have much time for observing them. They were able 

 to burrow in the sand without any difficulty, and fed by taking 

 up pellets of sand and passing them through the intestine. 



The body of this species is from 3 to 5 cm. in length, and the 

 proboscis is more than half as long as the body. Both the body 

 and proboscis may be extended to about twice the usual length 

 when the animal is feeding or moving about on the surface of 

 the sand. The diameter of the largest specimens measures 

 from 14 to 16 mm. The body is rather pointed at both ends, 

 and 2 short curved setse are borne from 5 to 10 mm. back of the 

 mouth on the ventral surface. The body wall is so thin that 

 the internal organs often may be seen through it. Small pa- 

 pillae are scattered over all parts of the body, but areTnost 

 numerous and prominent on the posterior region. 



As in Lampert's specimens, there are 13 bundles of longitu- 

 dinal muscles. Even in the largest specimens these are very 

 small and thin, and in the smaller and younger individuals they 

 cannot be detected by means of the microscope. 



Cross sections were made of the central part of the body wall 

 of 4 specimens ranging from the youngest to the oldest, in order 

 to compare the dermal muscle layers. In the youngest speci- 

 men the longitudinal muscle is continuous and of very nearly 

 uniform thickness. In the next individual there are 13 longi- 

 tudinal swellings of the longitudinal muscle, although it remains 

 continuous all the way around the body. In the third specimen 

 the bundles have become thicker, while between the bundles the 

 muscle has decreased considerably in thickness. In the fourth 

 and oldest specimen the longitudinal bundles are comparatively 

 thick, while the muscle between the bundles has become atten- 

 uated, as if it had been pulled out, until it has a thickness of 

 only one row of fibers in some places, and in others it even has 

 disappeared entirely. In all the sections the oblique muscle 

 layer is very thin, but it is continuous and uniform in thickness, 

 and follows the outline of the longitudinal muscles. In the 

 spaces in which that muscle is lacking, the oblique layer is 

 separated from the circular layer only by connective tissue. 



The color of the living worm is a rich brownish pink. The 

 presence of the longitudinal muscles is indicated in the larger 

 specimens by 13 white longitudinal lines. The proboscis is pale 

 cream color on the dorsum ; faint green lines run along the edges 



