374 



DISCOVERY REPORTS 



one-fifth to stage IV,which means that three-quarters of all specimens belong to stages II 

 and III. One cannot of course speak of an increase of pigmentation towards the depth 

 down to 750 m. Of Broch's 180 specimens thirty-eight are of type I, seventy-seven of 

 type II, forty-seven of type III, and eighteen of type IV. 



The Discovery material is mostly several years old and the pigment-bearing epi- 

 thelium often more or less broken away and the specimens faded. It was therefore in 

 many cases very difficult to place the specimens in respect of their pigmentation in one 

 of Broch's four groups. Strictly speaking, Broch's groups I and II are not represented 

 in the present series. Specimens with pigment on the stomach only, and occasionally on 



Table VI 

 Showing the bathymetrical distribution of the Discovery specimens of AtoUa wyvillei 

 arranged in the four colour groups (I-IV) of Broch. The figures denote numbers of 

 individuals. Closing net hauls only, with the exception of Sts. 270 and 282 



the gonads too, but otherwise transparent, are not present. Pigment is always to be found 

 besides on the stomach, on the peripheral zone, especially on the tentacle muscles and 

 in the subtentacular pockets. No specimens are found with pigment on stomach and 

 ring muscle only. The pigment on the ring muscle is very labile, and falls off' very easily 

 in the form of dark, irregularly formed large or small pieces of subumbrellar epithelium. 

 Even in the relatively few large dark specimens which I place in Broch's group III or IV 

 the ring muscle is only partially pigmented, and never fully covered with pigment. It 

 was difficult not only to place the faintly pigmented or faded specimens in Broch's 

 groups I or II, but also to place the dark specimens belonging to groups III or IV. In 

 many cases the gonads of the large specimens were not developed. It was therefore 



