172 ON AN EARTHWORM OF THE GENU8 BENHAMIA. [Feb. 20, 



from its ventral side. The diameter of this caecum is nearly, if 

 not quite, equal to that of the oesophagus itself. The accompanying 

 drawing (fig. 3, p. 171) shows the relations of this caecum during the 

 course of the oesophagus. The drawing represents a part of the 

 intersegmental septum dividing segments xii/xiii cut out of 

 the body and viewed from behind. Above are the dorsal (d.v.) 

 and supra-intestinal (s.i.) blood-vessels, the latter of rather 

 greater calibre than the former. The oesophagus (ce), and the 

 caecum (c), as will be seen, look like a single subdivided tube, the 

 former having a light fold projecting into its interior from below, 

 not to be compared therefore to a typhlosole. Below again to 

 this comes the ventral blood-vessel (v.v.) This oesophageal caecum 

 passes forward as far as to the xrth segment, where it appears to 

 end without any diminution of calibre. 



There are two structures among Earthworms with which this 

 median ventral oesophageal caecum may perhaps be compared. I 

 mention them in order of probability. Dr. Beuham described in 

 Perichceta seclgwicki ' — and 1 have been able to confirm 2 his state- 

 ment — that instead of the usual pair of caeca found in the species 

 of this genus, there was a single median ventral caecum, like the 

 paired ones in general appearance but not visible until the gut was 

 lifted up. 



More comparable, as I think, are the ventral '• Chylustascheu," 

 as they have been termed by Dr. Michaelsen, of the Eudrilidae. 



They are probably more comparable in that they are oesophageal 

 and not intestinal. Moreover, the fact that this species of 

 Benhamia has numerous iutestinal caeca, precisely comparable in 

 structure to the paired intestinal caeca of most Perichcehe, seems 

 to negative the former comparison. The position of this caecum, 

 on the other hand, fits in very well with the suggestion that it 

 represents, perhaps in an incipient form, the unpaired ventral 

 glands of Eudrilus, 1'olytoreutus, and other genera of Eudrilidae. 

 One difficulty in the way of this comparison is the greater extent 

 of the caecum in this Benhamia ; even where there are three 

 separate veutral calciferous glands in the Eudrilidae, they only 

 occupy a segment apiece, extending in their totality through 

 segments ix-xi. In the w orm which forms the subject of the 

 present remarks the caecum lies in segments xi-xv. On the 

 hypothesis, however, which is suggested, the differentiation of a 

 single caecum might easily result in the shortening of the total 

 area. The intercommunication of two of these glands in Poly- 

 toreutus (as an occasional variation) is an argument in favour of 

 the comparison urged here. In this case the unpaired ventral 

 caecum of Benhamia co'dfera will bear the same kind of relation to 

 the ventral unpaired glands of many Eudrilidae that the single 

 diverticulum of the enteron of Amphioxm does to the complex 

 liver of higher vertebrates. On the theory that the terrestrial 



1 Joum. Linn Soc, Zool. xxvi. p. 201. 



- " On a Collection of Earthworms from New Britain &c.," Willey's Zool. 

 Eesults, pt. ii. p. 184. 



