No. 2.] ANATOMY OF BDELLODRILUS ILLUMINATUS. 499 



haematoxylin gave the best general results. Biondi-Ehrlich 

 was particularly valuable for differentiating glands, for tracing 

 nerves among the muscles of the body-walls, and in studying 

 the testes and ovaries. Borax carmine occupied its usual im- 

 portant place among general stains. Methylene blue was also 

 used as a nerve tracer. The results obtained from a study of 

 many series of sections were further verified on living mate- 

 rial, mounted preparations of entire worms, and teased prepa- 

 rations. 



External fovjn. — The rounded club-shaped body is termi- 

 nated anteriorly by the so-called head, and posteriorly by the 

 sucker. The head is narrow and is less sharply distinguished 

 externally from the following segments, than is usual in the 

 family (Fig. i). It consists of four annuli, which, there is 

 reason to believe, represent as many somites. The first, or 

 peristomial annulus is divided into very mobile dorsal and ven- 

 tral lobes or lips, which exhibit slight median emarginations, 

 but are otherwise entire; and lack the sensory hairs and 

 papillae which are usual in this family. There is no pro- 

 stomium. The fourth cephalic annulus is very narrow; and 

 when the animal is contracted, is completely hidden beneath 

 the overlapping anterior margin of the first body somite, into 

 which it is drawn by the longitudinal muscles. The remaining 

 two, the second and third, appear externally as simple muscular 

 rings. 



The body proper consists of eight strongly bi-annulate 

 somites, posterior to which three crowded, but still obscurely 

 bi-annulate somites, form the posterior sucker and its support 

 (Fig. I, I to 11). These increase in diameter, gradually, from 

 the first to the seventh, and then decrease rapidly to the 

 posterior sucker, which is part of the eleventh somite. Each 

 of the body somites, with the exception of the last, is conspicu- 

 ously divided into an anterior major, and a posterior minor annu- 

 lus ; the former are much longer, as well as broader, than the 

 latter, and appear more prominently so the greater the degree 

 of contraction, which results from the peculiar manner in 

 which the minor annuli are telescoped within the anterior mar- 

 gins of the major annuli following, as well as to the more 



