358 



DISCOVERY REPORTS 



Table III 



Shozving the balhymetrical distribution of the different forms o/Periphylla 

 hyacinthina, S teens triip. Figures denote numbers of specimens 



* The depth of the specimen from St. 461 E is not indicated. 



Bigelow (1909, 1928) and Broch (1913) have stated already that there is a relation be- 

 tween the amount of pigmentation and the depth at which the medusa lives. From his 

 table 2, p. 6, Broch deduces the rule that the darker the specimens the deeper they 

 generally occur. This is right to a certain extent, but in my opinion it is no exact rule 

 and may not be generalized. The lighter dodecabostrycha stage lives in more superficial 

 strata than the darker hyacinthina and the darkest regina. All three stages of develop- 

 ment, however, occur also in the same layers (see Table III) : for instance, from 750 to 

 1000 m., 23 dodecabostrycha, 10 hyacinthina typica, i regifia; in the layer of 1250- 

 1500 m. I dodecabostrycha, 1 hyacinthina, 14 regina. The different degrees of pigmenta- 

 tion occur in one and the same stratum. 



Broch 's own table. No. 2, p. 6, reveals the same fact as ours. His figures are not at all 

 so convincing as he believes. For instance, between 500 and 600 m. 8 dodecabostrycha, 

 23 intermediates, 6 hyacinthina. In 700-800 m. and looo-i 100 m. there are much more 

 intermediates than hyacinthina typica, and the hauls from i250-i5oom. only show 

 higher numbers in favour of the hyacinthina type. It is, however, a mistake to take the 

 actual numbers of collected specimens instead of percentages. If regarded in this way 

 then in fact the pigmentation increases ivith the depth as seen in Table IV modified after 

 Broch. In the table regina is not included because the species is treated by Broch 

 separately. He could find no difference whatever in colour between hyacinthina and 

 regina. 



Similarly Broch traces an increase in size towards deep water (p. 7). I believe, how- 

 ever, that his table 3 on hyacinthina gives him no right to draw this conclusion . According 

 to Broch all large specimens ought to be found in the greatest depth. This, however, is 

 not the case. In his haul from 1500 m. there are more small specimens than large ones. 



