266 



THOS. H. MONTGOMERT, 



the body there is, accordingly, a single row of nephridia, these organs 

 being situated one behind the other, this row extending from nearly 

 the tip of the head to the posterior commissure of the blood vessels ; 

 in other words, a portion of the most anterior nephridium, on each 

 side of the body, is situated a considerable distance anterior to the 

 brain, while the posterior end of the last reaches almost to the anal 

 region of the body. This arrangement is more clearly explained by 

 reference to the diagrammatic Fig. 9 : in this diagram, the dotted line 

 represents the outline of the body, while the heavy black lines re- 

 produce the main nephridial ducts. The fact is worth notice, that in 

 no other Nemertean do the nephridia extend so close to the posterior 

 end of the body. 



These details were deduced from the study of a nearly perfect 

 series of cross-sections of an unusually large specimen of the species, 

 a series of from 1300 to 1400 sections, each section of 3 /< thickness. 

 Now since the nephridia of one side never pass across to the other 

 side of the body, then whenever I found a number of consecutive 

 sections, where on one side of the body no traces of these organs 

 were present, I could conclude with certainty, that here was a space 

 dividing two nephridial ducts. And thus, having found 9 such spaces 

 on the right, and 7 on the left, tlie number of nephridia on the right 

 was found to be 10, and 8 on the left. 



The length of a space between two neighboring nephridia varied 

 from 6 /< to 63 /< ; these distances averaged larger on the left than 

 on the right side. Of course these figures, as well as others which 

 are to follow, are only relatively correct, since in the fully extended 

 worm they would necessarily be greater than in its somewhat con- 

 tracted state, after fixation in corrosive sublimate. The lengths of 

 the several nephridia themselves, which are represented relatively in 

 Fig. 9, I found to be as follows: 



