1901.] NATURAL SCIENCES OF THILADELPHIA. 661 



males and females; (3) that the color of the inteslinal cieca is de- 

 pendent upon the amount and character of the food contents. The 

 intestine in freshly taken worms is much darker in color than in 

 specimens that have been kept in an aquarium for several days 

 without food. 



The caudicle in life appears as a slender white thread at the 

 posterior end of the body, figs. 4, 5, 6. It is usually much 

 twisted and is easily broken oft". It should be mentioned here that 

 in none of the four specimens that were first obtained in 1899 was 

 the caudicle preserved, so that the presence of this appendage is 

 not mentioned in my preliminary note, Thompson (1900 a). 



The wdiite spots in the posterior part of the worm, slightly exag- 

 gerated in fig. 6, are parasites and will be described under that 

 heading. 



On account of its transparency the living worm is a most favor- 

 able and interesting object for study with the low powers of the 

 microscope. It should first be slightly stupefied to prevent exces- 

 sive movements and contractions, so that when it is placed on the 

 slide with a few drops of sea-water and covered, the muscles 

 relax and it lies quietly there, fully extended. With a magnifica- 

 tion of about 70 diameters, it is possible to study the brain lobes and 

 commissures, the cerebral organs, the blood vessels of the head, 

 the proboscis and rhyuchoda}um, the alimentary system and the 

 gonads. In only two cases could the nephridia be distinguished, 

 but nothing was determined as to their structure. Several attempts 

 were made to study the worm by treatment with methylen blue, 

 after the method of Burger (1891, p. 327, footnote), but without 

 success. 



The results obtained from the study of the organs in life will be 

 incorporated in the several sections relating to the different organ 

 systems. 



II. Anatomy. 



Body Wall.— a. Body Epithelium. — The body epithelium, fig. 

 2, is a high one-celled layer, consisting of ciliated supporting cells, 

 S.C, and gland cells, Gl.-i, GL^, resting upon a basement layer, 

 B.L. Interstitial connective tissue cells are always present in 

 varying numbers between the bases of the epithelial elements. 



The supporting cells, fig. 1-1, are about .035 mm. in height, 



