H "TERRA NOVA" EXPEDITION. 



remains iu every respect similar to its near relatives, nearly all of which are earth- 

 worms, or to a certain extent aquatic. 



The worms occur in considerable numbers, lying on and among the gills of the 

 crab, and also upon the lining of the dorsal wall of the gill-chambers. The lining is 

 here modified in these crabs into a richly vascular area, or " lung," by means of which 

 oxygen can be absorbed from the air ; this adaptation being in accordance with the 

 crab's habit of living on dry land for the greater part of the year. So far as is known 

 from observations in other localities, the land-crabs only repair to the sea for a few 

 days at one period of the year, for the purpose of allowing the larvae to escape from 

 the eo-o-s into the water. The crabs in which the worms occurred were collected, as 



Oo 



Surgeon Atkinson informs me, at " 1,500-2,000 feet above sea line," (i.e., within 20 feet 

 of the highest point of the island), and were " feeding on decaying vegetation and 

 perhaps a certain amount of excreta from sea-birds." 



It would appear that the worms must be capable of withstanding exposure to sea- 

 water at least for a short time each year, unless they only migrate into the crabs' 

 gill-chambers during the period of terrestrial life. This, however, seems improbable. 

 Worms of various ages and at various stages of development, besides fully adult- 

 individuals, occurred in the gill-chambers of a preserved crab in the " Terra Nova " 

 collection,* which, by the kindness of Dr. W. T. Caiman, I was permitted to examine. 

 From this fact it may be inferred that they probably spend the whole of their lives in 

 this situation. It would be of the greatest interest to know what advantage they 

 derive from the crab whether mere protection from enemies, or some special food. It 

 is indeed impossible to state upon what nutriment they subsist ; it seems improbable 

 that they are capable of extracting blood from the crab's gills or from the vascular 

 epithelium, their mouths being provided with no hard parts which would enable them 

 to make punctures. 



These questions must for the present remain unanswered, since answers to them 

 can hardly be derived from the examination of spirit-specimens. 



II.-SYSTEMATIC. 



Morphologically, there seems to be no reasonable ground for the erection of a new 

 genus for this worm. It appears to approach closely to the described species of 

 Enchytneus, differing only in details of size, arrangement of bristles, and other small 

 points ; for the present, therefore, it may be placed in that genus. 



* It is also worthy of notice that I found specimens of the same worm in individuals of Gecarcinus 

 latjostoma collected in South Trinidad (a) by the " Discovery " expedition and (6) by the late Major G. E. 

 H. Barrett-Hamilton's expedition to South Georgia. The occurrence of the worms seems, therefore, to 

 be quite common. I have no evidence of the existence of the same worm in crabs from other localities, 

 but a closely-related species occurred in G. quailratus, from Clarion Island. Of this species I hope to 

 publish an account elsewhere. 



