December 9, 1922] 



NA TURE 



789 



time flattening the fins close in to the posterior end, 

 approximately as shown in the preserved specimen, 

 Fig. 2. Less frequently Spirula was observed in the 

 aquarium making a forward rush with its head to 

 the front — i.e. without reversing the funnel. It is 

 possible, however, that this latter mode of progress 

 is the usual one — for example, when in pursuit of 



Prey- 

 In addition to these jerky movements, the animal 

 also makes others at a slower rate. It may often be 

 seen in the aquarium moving vertically downwards 

 from the surface, head first. During the descent 

 the fins are held vertical (see Fig. i) and move with 

 a rapid waving or fluttering motion which, in con- 

 junction with the current of water from the funnel, 

 now facing upwards (to the rear), carries the animal 

 down towards the bottom. Sometimes it will come 

 to a standstill in mid-water, at others it will not 

 stop until it has reached the bottom, but so long as 

 it remains below the surface the fins are kept in 

 motion as described, and the funnel is pointed 

 upwards. It may rise again slowly to the surface 

 without altering its vertical position ; the fins are 

 then sometimes seen in motion, sometimes pressed in 

 close to the hinder end. 



In order to ascertain whether this movement of 

 the fins was necessary to maintain the animal in 

 the vertical position, which it adopted for the most 

 part in our aquaria, we cut off one of the fins from 

 a specimen, selecting a large and powerful individual 

 for the purpose. It was at once evident that the 

 lack of a fin in no way affected the maintenance of 

 the vertical position ; what did result was that the 

 animal was now unable to keep under water. When 

 placed at the bottom of the aquarium, it invariably 

 rose again to the surface. On one occasion, when 

 guiding it to the bottom, we happened to bring the 

 creature into contact with the glass wall, when 

 something new was seen. On touching the wall, it 

 spread out its arms and clung to the glass, and was 

 now able to keep under water. We tried to move 

 it away from the glass by prodding it with the handle 

 of a lancet. It relinquished its hold, but only to 

 attach itself to the lancet handle in the same way. 

 Evidentlv the eight short arms are highly sensitive 

 to touch — the two longer less so, if at all. On this 

 occasion also we had a sight of the animal's black, 

 horny beak, and learned that it is capable of inflicting 

 a powerful bite, as the handle of the lancet showed. 



When left to itself the Spirula will remain suspended 

 for hours at the surface, or lower down in the water, 

 always in a vertical position, and with arms more 

 or less closed in. When violently disturbed, the 

 animal may occasionally discharge a small cloud of 

 greyish ink. We managed to keep some specimens 

 alive for more than two days in our small aquaria, 

 with no aeration of the water. Generally, however, 

 they lived onlv a little more than a day. 



On several occasions we were able to perceive that 

 the small bead - like organ at the posterior end is a 

 light organ. It emits a pale, yellowish-green light, 

 which, from the normal position of the animal in the 

 water, is directed upward. In contrast to the light 

 displayed by so many other marine organisms 

 (crustacea, etc.), which flares up and fades away 

 again, the Spirula's little lamp burns continuously. 

 We have seen the light showing uninterruptedly for 

 hours together. 



Mode of Life. — The third Dana expedition has made 

 captures of Spirula in 65 hauls from 44 stations, and 

 in every case with implements used pelagically, 

 without touching the bottom. The depths at which 

 our specimens were taken varied from about 2-300 

 metres to about 2000. The greatest quantities were 

 found at depths from 300 to 500 metres ; none were 



NO. 2771, VOL. I IO] 



taken in the upper 200 metres of the sea, though the 

 nets were constantly drawn within this range. 



Our investigations thus indicate that the species 

 is bathypelagic, i.e. pelagic in deeper water lavers, 

 and so confirm the supposition advanced by J. Hjort 

 (Murray and Hjort, " Depths of the Ocean," p. 595, 

 London, 1910). A. Agassiz ("Three Cruises of the 

 Blake," ii. p. 61, Boston and New York, 1888), who 

 has examined a specimen of Spirula " dredged . . . 

 from a depth of 950 fathoms," is of opinion that 

 " from the condition of the chromatophores of the 

 body, it evidently lives with its posterior extremity 

 buried to a certain extent in the mud." This con- 

 clusion is doubtless erroneous. It would be un- 

 reasonable to suppose that the creature should thus 

 bury its hinder part — which is lighter, owing to the 

 shell, and also carries the light organ — in the bottom. 

 It seems far more likely that the specimen brought 

 up in the Blake's dredge was not taken from the 

 bottom at all, but captured higher up in the water 

 when hauling in. 



Size, etc. — The 95 specimens of the third Dana 

 expedition vary in length from 5 to 47 millimetres 

 (maximal length of the mantle). On arranging the 

 measurements graphically, they fall more or less 

 evenly distributed along the millimetre scale, with 

 nothing to suggest the presence of different " year- 

 classes " in the material. Judging from this, it might 

 seem as if the propagation of the species was not 

 restricted to a short period of the year. 



At one station (St. 1157, N. of Cape Verde Islands) 

 we found the following : — 



Depth (in metres). 



250 . 



300 . 



500 . 



IOOO . 



Length of specimens 

 (in millimetres). 

 9, 17, 20, 22 



7, 17, 20, 21, 22, 2; 



15, 41 



7, 15, 19, 22 



At other stations, specimens more than 40 mm. 

 long were found both in the deepest hauls and in 

 those nearest the surface of all the hauls containing 

 Spirula. 



The spscies seems" to attain maturity at a length 

 of about 30 mm. (length of mantle). At this length 

 the males begin to be hectocotylised, and the 

 specimens more than 30 mm. which we opened were 

 found to have mature sex organs (the females with 

 large, oblong, honey-coloured ova, besides smaller 

 eggs). 



As previously mentioned, the Spirula has a 

 chambered inner shell. As the animal grows the 

 number of chambers increases, and a turn of the shell 

 takes place. The figures below show how the number 

 of chambers increases with growth of the animal. 



38 . . -34 (mature male) 



44 . . .38 (mature female) 



Approximately, then — but only approximately — 

 an increase of one millimetre in length answers to 

 the formation of one fresh chamber. 



While the Dana was at the Virgin Islands in the 

 West Indies (St. Thomas and St. Croix), as also at 

 Bermuda, we often found considerable numbers of 

 Spirula shells on the shore. Most of the shells were 

 damaged, but so far as could be determined the 

 intact specimens generally had between 30 and 40 

 chambers, i.e. representing, from the above, fully- 

 grown mature specimens. From this I must conclude 

 that at any rate the bulk of the shells found washed 

 up on the coasts are those of fully-grown Spirula 



