THE VISCERAL MASS IN ANTEDON ROSACEUS. 301 



thing in itself and looks so little like a mere part of an organism that 

 a specimen of the isolated visceral mass of one species of Comatula 

 was once described as a distinct animal. The dorsal surface of the 

 visceral mass, that is the one resting on the calyx, is covered by a 

 compact layer of connective tissue, which has a silky appearance on 

 the outside. In the centre of the dorsal surface is a minute hole 

 which serves for the passage of the central plexus of blood vessels 

 from the chambered organ into the visceral mass. The ventral sur- 

 face is covered by epidermis overlying connective tissue, and has the 

 mouth in the centre and the anal cone at one side. This layer of 

 epidermis and connective tissue, covering the ventral surface of the 

 visceral mass, has been called by Carpenter the " oral perisome," and 

 is continuous with a similar layer of tissue clothing the ventral sur- 

 face of each arm. 



The Process of Evisceration. — In some specimens of Antedon 

 rosaceus the visceral mass is very easily removed from the calyx by 

 pushing it aside with a blunt needle ; but it is a noteworthy fact that 

 this evisceration cannot be effected with equal ease in all cases, for, 

 while in some specimens the visceral mass comes away almost with 

 a touch, in others it adheres firmly to the calyx and cannot be brought 

 away at all except by tearing it to pieces. 



While at Millport, I observed that specimens were dredged up by 

 the steam launch "Medusa," which had already lost their visceral 

 masses. At first I was inclined to think that the animals cast them 

 out of their own accord on being irritated, as some Holothurians cast 

 out their intestines, but this must be regarded as very doubtful, for, 

 owing to the slight manner in which they are generally attached to 

 the calyx the visceral masses might have been torn out by rough 

 treatment in the dredge. This view is perhaps supported by the fact 

 that isolated visceral masses have themselves occasionally been 

 dredged up. 1 



But although this evisceration is probably in most cases effected by 

 the dredge, yet I have very strong reason for believing that eviscera- 

 tion and subsequent regeneration of the lost visceral mass occasionally 

 occur quite independently of dredging operations. I have in my pos- 

 session a specimen of Antedon rosaceus, from the Firth of Clyde, in 

 which the visceral mass shows clear traces of having been regenerated; 



1 Challenger Report, Nan: of Cruise, vol. I., Pt. I., p. 311. 



