660 PROCEEDINGS OF THE ACADEMY OF [DeC, 



vidual that in rest measured 6-8 cm. may now be 10-12 cm. or 

 longer. 



A change in color accompanies the elongation. At rest 

 the body has a decidedly pink color ; in extension the body is more 

 transparent and dull brownish. This may be seen by comparing 

 the extended worm in fig. 4 with figs. 5 and 6. As the pink color 

 is most pronounced in the contracted condition, becomes less so at 

 rest and disappears in extension, it is probably due to muscular 

 contraction. The width varies in different specimens from 

 1^3 mm. ; it also varies in the same specimen according to the 

 state of contraction. 



In the living worm, PJ. XL, figs. 4, 5, 6, four different re- 

 gions may be distinguished: (1) the head, (2) the anterior part 

 of the body, (3) the posterior part of the body, and (4) the 

 caudicle. 



The head is about 6 mm. long, not sepai'ated from the body, 

 pure white and tapering to a very fine point. There are no lateral 

 slits, the ciliated pits of the cerebral organs opening directly to the 

 exterior. The mouth is a very small round opening on the ven- 

 tral surface. The shape and color of the head, together with the 

 absence of lateral slits, are good criteria for determining the genus. 



The anterior part of the body is the region extending from the 

 mouth to the beginning of the lobed middle intestine. The length 

 is from 1^3^ cm., and the color varies from pale yellow to pink- 

 ish. It is rounded and more or less swollen, owing to the presence 

 there of the greater part of the proboscis. 



The posterior part of the body is the most extensive. It is 

 somewhat flattened in life but is always rounded in preserved speci- 

 mens. The color varies from rose color to pale yellow, light 

 brown and chocolate brown, A pinkish median line on the dorsal 

 surface represents the rhynchoco}! ; the alternating cross lines of 

 light and dark on each side of the median line, fig. 5, are the 

 gonads and intestinal cseca respectively. 



A series of observations were made to ascertain if there are 

 any appreciable color variations corresponding with sexual ma- 

 turity or difference of sex. The conclusions reached are (1) that 

 there is no difference in the color of sexually mature and immature 

 individuals, except that the increased size of the gonads in the 

 mature specimen causes the cross lines mentioned above to be more 

 pronounced; (2) that the general color of the body is the same for 



