Benham . — Bifurcation in Lumbricus rubellus. 187 



on the branch occui on the inner side of the 3rd segment (corresponding 

 to the 6th clitellar segment). Possibly they are also present on the pre- 

 ceding segments, embedded in the skin ; but there are none on the rest of 

 the branch. 



At the end of the branch is a slight pit, which suggests that an anus is 

 present here ; it is, however, imperforate ; and on opening the branch 

 at two places I find that the intestine does not enter it, but the nerve-cord 

 and the nephridia are continued to the end of it. 



It is, of course, difficult, if not impossible, to say how this bifurcation 

 or branching has come about in the free state. It may be that the worm was 

 injured at the commencement of the clitellar region, and that a lateral 

 outgrowth developed instead of a mere healing of that wound. 



The specimen is remarkable not only on account of the forward situation 

 of the bifurcation, but also on account of the great inequality in size between 

 the two forks, and finally on account of the absence of the intestine in the 

 smaller branch. 



II. In 1886 Mr. T. W. Kirk described and figured a " Curious Double 

 Worm.'** This specimen remained in the Dominion Museum till about 

 two years ago, when the late Director, Mr. A. Hamilton, was good enough 

 to send it to me for examination. When it reached me it was glued to a 

 piece of card. It was evident that at some time it had become dry, owing 

 to the evaporation of the alcohol, for the tails are shrunken and the skin 

 a good deal shrivelled. However, it is in sufficiently fair preservation for 

 me to add something to Mr. Kirk's account. 



A re-examination of this specimen seemed desirable, for Mr. Kirk was 

 one of the first to place on record the occurrence of a bifurcated worm, the 

 only previous accounts being those of Asa Fitch in America in 1865 (in a 

 report on insects in the State of New York), C. Robertson in England in 

 1867, and Bell in 1885. It is evident that Kirk did not know of either of 

 these. A fair number of similar cases have been recorded since that time, 

 but Kirk's paper has been overlooked bv all these writers, even by the most 

 recent, Korschelt (1914). 



The worm is a species of the genus Octochaetus, though, as it is immature, 

 it is impossible to define its specific position. Kirk recognized that it was 

 not a Lumbricid, but a native, though he figures the prostomium as being 

 like that of L/nnbricns— " tanylobic," whereas it is " epilobic," without 

 the prolongation into the 1st segment. The chaetae are all on the ventral 

 surface, small in size and close together, so close that each couple looks 

 at first like a single bristle. The lines are approximately equidistant, though 

 the two ventral rows are rather farther apart than the lateral row is from 

 the ventral of its own side. 



Kirk's measurements may be given in his own words : * The anterior 

 ] Million is about 1 in. in length and ^ in. in diameter. . . . From the 

 posterior end of the thick part, which terminates abruptly, spring two limbs, 

 each 2| in. in length and of an average diameter of ^ in." 



At present the " body " measures 14 mm. in length by 6 mm. in diameter ; 

 the two tu tails " are unequal, one measuring 33 mm., the other 40 mm., 

 each with a diameter of about 2-5 mm. These two tails are curved and 

 undulating, a good deal shrunken, and one came away from the body on 

 the specimen being removed from the card. 



* Trans. X.Z. hist., vol. 19, p. 64. 



