Benham. — Oligochcsta from the Southern Islands. 293 



character of the peristomium. The chsetee commence in the 

 2nd segment. This and the following segments are perfectly 

 normal : there is no indication of a double set of cheetse in any 

 of them. There is no furrow in the 1st or 2nd or any subsequent 

 segment to suggest a fusion of two segments ; in fact, the seg- 

 ments are not annulated, as is sometimes the case. The worms 

 are fairly soft, not contracted at all, so that the limits of the 

 segments are quite distinct and definite. There seems no possi- 

 bility of error in the enumeration of the segments such as does 

 occur in a strongly annulated worm (e.g., Octochcetus). There 

 seems to be no means of explaining the peculiarity from an 

 external examination. Internally, too, the septa, though thin, 

 are quite distinct. There is none of that shifting of septa that 

 occurs in many large worms ; and, as the soft condition per- 

 mitted it to be fully extended, there is no crowding of the septa. 

 Repeated countings, both externally and internally, gave the 

 same result — viz., the ovaries (fortunately large and readily seen) 

 in segment 12, and other organs one segment forward. There is 

 no " spiral segment " such as has been observed by Morgan and 

 others. Longitudinal sections show that the cerebral ganglia 

 occupy the normal position at the hinder part of the 3rd seg- 

 ment ; the circumpharyngeal commissure lies in this segment, 

 and the first ventral ganglion occupies the anterior half of the 

 4th segment, and a single ganglion corresponds to each of the 

 subsequent segments. 



The condition of preservation is not sufficiently good to 

 enable me, with certainty, to study the detailed distribution of 

 the ganglion-cells in the first ventral ganglion ; but, from a con- 

 sideration of the facts, the only way to explain the shifting of 

 the organs is to imagine an " excalation " of a segment in front 

 of the testes : if the spermatheca has been unaffected, then the 

 original 9th segment has disappeared ; or if the spermatheca has 

 been moved forwards, then one segment lying between the 2nd 

 and 8th has disappeared ; but as the gizzard is in the 6th 

 segment the former suggestion is the more probable. If we had 

 had only a single individual this peculiar forward shift would 

 have been remarkable enough, and might have been explained 

 by supposing that the anterior extremity had been cut off, and 

 that an imperfect regeneration of segments had followed — a 

 regeneration in which one segment short of the full number had 

 been formed ; but when two individuals exhibit exactly the same 

 phenomenon it does not seem possible to refer it to regenera- 

 tion. Nevertheless, I do not consider it necessary to form a new 

 genus for the reception of the worm — as we should have done a 

 few years back — for in all essential structural points it agrees so 

 closely with species of Bhododrilus that it must be looked upon 



