July 7, 1911] 



8CIENGW 



purea. Adults 6i the former group were most 

 abundant below 500 meters, larvse (Acanthe- 

 phyra) alone were taken in the upper layers 

 of water. The oldest specimens were from 

 the deepest layers, down 1,500 m., and the 

 depth zones for corresponding sizes were 

 deeper on the southern than on the northern 

 lines. The second group, on the other hand, 

 reaches its maximum higher up, at about 

 500 m., but here too the older specimens were 

 found deeper on the southern than on the 

 northern lines. 



As a rule black and red forms prevail among 

 the larger inhabitants of the intermediate 

 waters. This rule is not absolute, since two 

 species of black fishes were found within 

 150 m. of the surface. But these two, like 

 Gyclothone signata, have highly developed 

 light organs. And it is even more significant 

 that all the captures of them from depths less 

 than 500 m. were made at night; furthermore, 

 as Dr. Hjort points out, there are previous 

 records of black fishes, e. g., Idiacanthus and 

 Asironesihes, being taken close to the surface 

 at night. 



Experiments on the penetration of light, 

 carried on by means of an improved photom- 

 eter, devised by Dr. Helland-Hansen, showed 

 that there is a close correlation between the 

 lower limits of light of different colors and 

 the vertical occurrence of the black fishes and 

 red prawns. 0£E the Azores the blue and 

 violet rays were still detected at 500 meters, 

 though the red had been absorbed entirely; 

 at 1,000 meters the ultra-violet rays were still 

 perceptible, but at 1,700 no trace of light was 

 found. That is to say, prawns and black 

 fishes, in the day time, are confined to a zone 

 below the penetration of red light: it is only 

 at night that the fish with large light organs 

 are found higher up in the water. While 

 their upper limit is higher in high than in 

 low latitudes, the same must, on physical 

 grounds, be true of the penetration of light. 

 Furthermore, the theoretical calculations of 

 the penetration of light at different latitudes 

 shows that it agrees very well with the upper 

 limits of the red prawns from the lines of the 

 Michael Sars and from the Norwegian Sea. 



At a higher level than that occupied by the 

 red and black forms, where sunlight is appre- 

 ciable, i. e., with a lower limit, in temperate 

 latitudes, of say 500 m. ; and a maximum at 

 about 300 m. is a totally distinct fish fauna, 

 characterized by lateral compression, larger 

 and often telescopic eyes, large light organs 

 and silvery sides, examples being afforded by 

 Argyropelecus and by various Sternoptychidse 

 and StomiatidaB. 



These observations rest on such a mass of 

 data that they seem altogether worthy of ac- 

 ceptance. They form one of the most impor- 

 tant of recent additions to oceanic biology. 

 They are of special interest to the reviewer 

 because of his studies on the medusse of the 

 intermediate waters collected by the Albatross. 

 Among the latter, as among the fishes, there 

 are two distinct color groups, one slightly 

 pigmented, if at all, but iridescent; the other 

 densely pigmented with red or brown. Both 

 have numerous representatives. Our knowl- 

 edge of their vertical occurrence is still 

 scanty; but we know that they do not nor- 

 mally come to the surface, except in very high 

 latitudes. On the other hand, they are by ne 

 means confined to abyssal depths. The im- 

 portant question in connection with Dr. 

 Hjort's article is whether the two color- 

 groups of medusae correspond to the two 

 color-groups of fishes in their bathymetrie 

 occurrence. To this an answer can not be 

 given definitely as yet. I have already sug- 

 gested^ that it is light which demarks their 

 upper limit as a whole. And it is at least 

 suggestive that at one station in the eastern 

 tropical Pacific the Alhatross took 3 genera of 

 " red " medusae in a Tanner closing net at 

 400 fathoms (one of them being also taken in 

 an open net from 300 fathoms), but none of 

 the " iridescent " group, while at the same 

 station two " iridescent " genera were taken 

 in the closing net from 300 fathoms, and two 

 others in the open net from the same depth. 

 These records suggest that at this station, at 

 least, the red medusae occurred as a whole be- 

 low the iridescent ones, but that the two over- 

 lapped at, say, 300-250 fathoms. One may 



- Mem. Mus. Comp. Zool., Vol. 37. 



