222 Mr. II. C. Williamson on a Bifid Earthworm. 



somites which are interposed between the trunk and its 

 thin connexion. This specimen (Fitch's) differs from the 

 one described here in that in the latter the left appendage is 

 of the same diameter as the trunk, and the right appendage 

 arises from the fiftj-fourth segment, not from the suture 

 between two segments. Fitch considered that in his 

 specimen the left appendage was the continuation of the 

 trunk, and this appears to be the case in the Lumhricus here 

 described. The right appendage arises from the right side of 

 the fifty-fourth segment (fig. 2). Segment 54 diflfers very 

 much from tiie other segments both in shape and size. It is 

 triangular in shape, the base being represented by the right 

 side, where the right appendage joins the segment (fig. 2). 

 The somite is of normal lengtli on the left side, but on the 

 right it has grown antero-posteriorly and is very much 

 longer. The increase in length on the right side has caused 

 the left appendage to be pushed to the left, so that the 

 anterior and left posterior portions are not in the same straight 

 line as they probably ought to be. 



At what time in the life of the worm the extra tail was 

 developed it is very difficult to tell. If it originated in the 

 embryo we should expect that the two tails would be similar 

 in every respect. They are not, however, identically equal. 

 The mode of connexion between the trunk and the right 

 appendage differs from that of the trunk and the left 

 appendage. The right-hand appendage, moreover, is con- 

 stricted at its junction with the anterior portion, while the 

 left is not so. The dorsal line is not present in the right 

 appendage. It is difficult to imagine how such an abnor- 

 mality could have originated in the embryo. In such a case 

 a division of each of the mesoblasts, neuroblasts, nephridio- 

 blasts, &c. must have been effected. It might appear 

 possible that the two appendages had been formed by a 

 median vertical longitudinal fission of the orii^inal worm. The 

 division may be supposed to have extended from the anus 

 forward to about the middle of the body dividing the gut, 

 vessels, &c. equally and passing between the two nerve-cords. 

 But the completeness of every organ in each appendage does 

 not countenance that supposition; but, assuming that such a 

 fission had taken place, it might probably have been going 

 on at the time of the death of the earthworm. In this case 

 there would have been at the fork a mass of embryonic cells, 

 by their division giving rise to the left wall of the gut in 

 the right appendage and tlie right wall of the gut in the left 

 appendage, and similarly with the blood-vessels, nerves, and 

 body-walls. The outer gut-walls of the two appendages 



