March 17, 192 1] 



NATURE 



77 



especially in the summer, and in Danish waters 

 during autumn ; it has also been found near Iceland 

 and off the northernmost coast of Norway (about 

 latitude 70° N.). It is thus not difficult to pro- 

 cure specimens, and such are also to be seen in 

 most museums. The oblong sun-fish [Ranzania 

 truncata), on the other hand, is far more rarely 

 seen in collections. It does not penetrate so far 

 to the north as Mola rotunda, but has, never- 

 theless, been found occasionally in the waters of 

 Western Europe and the British Isles, where its 

 northern limit of occurrence appears to lie. 



With regard to the habits of the oblong sun- 

 fish (Ranzania) practically nothing is known. It 

 may, however, be mentioned that it was on one 

 occasion observed in enormous numbers at the 

 surface of the water, at Martinique, in the West 



Fig. 4. — The (jWcwc sun-fish {Kanzan a iiuniata), 

 larval stages. Length, a, I'j mm. ; i, i "8 mm. ; 

 c, 2 '4 mm. ; a hatched on bo^rd the Dana in the 

 Sargasso Sea. 



Indies. The short sun-fish is quite frequently 

 encountered by mariners in the .Atlantic. I have 

 myself, on my cruises there, often seen it lying 

 half sideways at the surface, with the tall dorsal 

 fin projecting out of the water. It is not infre- 

 quently captured in the Mediterranean, especially 

 during summer in the Straits of Messina, and it 

 is known to feed on small forms of pelagic life. 

 A fact of interest is that the larva; of the fresh- 

 w-ater eel appear to be its favourite food. The 

 stomach, when opened, will often be found to 

 contain eel larvae (LeptocephaJus hrevirostris) by 

 the hundred. There can thus be little doubt that 

 it is one of the eel's deadliest enemies. The sun- 

 fishes appear to be highly prolific. In a specimen 

 of Mola rotunda j^ metres long, for instance, the 

 NO. 2681, VOL. 107] 



ovary was found to contain no fewer than 300 

 million small unripe ova. 



The method of propagation of the sun-fishes, 

 however, is unknown, and the tiny stages have 

 not been identified in the case of any species. The 

 collections made by the Danish Committee for 

 the Study of the Sea have often brought 

 to light larvae which I 

 sun-fishes, but it was 

 mine to which species 

 the trans-Atlantic cruise 

 summer of 1920, however, I succeeded in throwing 

 light on the question, and was able to follow the 



had to refer to the 

 impossible to deter- 

 they belonged. On 

 of the Dana in the 



Fio. 5. — Afoiti lanceolata (a and c), Ranzania trvncata (b)\ 

 c larval, a and b po«t-Iarval stagfs. Length, «, 5's mm. ; 

 h, 3'5 nim. ; r. 2 8 mm. ; a and h same enlargtment, 

 c more enlarged. Note that the tail has disappeared in 

 a and b. 



development of two species for a great way back : 

 in the case of one, to the ^^% itself. A full 

 account of this needs a mass of illustration and 

 proof material which would be out of place here. 

 I will therefore merely give a few illustrations, 

 reproduced from photographs, adding thereto 

 some remarks on these larval forms, which, be- 

 cause of their odd appearance, are probably with- 

 out parallel among fishes. 



Fig. 4, a, shows a larva of the oblong sun-fish 

 {Ranzania triincata), about 1-7 mm. long. It was 

 hatched on board the Dana in the Sargasso Sea. 



