STEXJCTURE OF EARTHWORM ALLIED TO NEMERTODRILUS. 557 



blood-vessel through more than two or three consecutive 

 sections without finding coagulated blood in its interior ; and 

 it is not difficult in well-preserved earthworms to detect the 

 blood-clots, nor is it easy to confuse them with any other 

 structures as a general rule. 



The tubes that I have referred to consist of larger trunks 

 with a definite arrangement, and smaller vessels which form a 

 plexus ; the longitudinal and circular muscular coats were per- 

 meated by thera. It is, perhaps, necessary to explain here 

 that the tubes in question have nothing to do with the 

 " Lyraphspaltraume " which Dr. Kiikenthal has figured and 

 described in certain Oligochseta, particularly in Tubif ex ; I 

 have met with spaces similar to those, and crowded with lymph- 

 corpuscles, in various genera of earthworms. I found them to 

 be particularly abundant in the two genera Heliodrilus and 

 Hyperiodrilus described in a recent number of this Journal 

 (1). They consisted in those genera, as Dr. Kiikenthal has 

 pointed out for other forms, of spaces, with no special walls, 

 between the muscular fibres. I quite agree with Dr. Kiiken- 

 thal in regarding these as the first beginning of the lymphatic 

 system of the Vertebrata, in which group the finest branches 

 of the lymphatic system are without intrinsic walls. The 

 tubes which I describe here have definite though thin walls, 

 darkly stained by borax carmine ; the substance of which they 

 are composed is granular in appearance, and there are evident 

 nuclei attached here and there to the outside of the walls. The 

 principal trunks run in a longitudinal and a transverse direc- 

 tion ; there are four main longitudinal trunks, which 

 run on a level with the four pairs of setsej they are 

 continuous from segment to segment. 



These tubes are of considerable calibre, almost equal in 

 diameter to one of the setae, or even greater; it is not particu- 

 larly useful to give accurate measurements of them, for the 

 reason that they varied considerably in size from place to 

 place, contracting here and expanding there. Their walls are 

 thin, but quite as thick as those of blood-vessels of about the 

 same size, 



