ATLANT. DEEP-SEA EXPED. 1910. VOL. III]. 



CEPHALOPODA. 



11 



Stat. 42. 300 m. w. Two young specimens, dorsal 

 mantle-length 16 and 18 mm. 

 „ 44. 4000 — Specimen with a dorsal mantle- 

 length of 23 mm. 

 „ 45. 3000 — Largest specimen, dorsal 

 mantle-length 26 mm. 



I have not yet examined the internal anatomy of the 

 larvae, and describe only their external appearance, which 

 confirms Joubin's description, also founded on external 

 characters, and in certain respects completes it. 



The youngest larva (pi. I, figs. 1,2) is, like the other 

 larvae, well preserved, and having been kept in formalin 

 exhibits no shrinking of the mantle. It has a barrel-like 

 somewhat clumsy shape, and at the posterior end of the 

 body we can on the outside see 5 chambers projecting. 

 As mentioned by Joubin in the case of his specimen, the 

 latter are entirely covered by the mantle, which however 

 is very thin just over the chambers. We may further 

 notice the fact that the posterior part exhibits no thick- 

 ening and also no obvious pigmentation. The edge of 

 the mantle is very clean-cut, and shows as yet no traces 

 of dorsal and ventral angles in the mantle. Particularly 

 interesting are the small size and the position of the fins. 

 They are spatular in shape, 0-6 mm. broad, and separated 

 from each other by the entire breadth of the chambers. 

 Their bases run obtusely to the axis of the body and do 

 not reach the posterior end, which is never overlapped 

 by the small fins. 



The head section of our larva protrudes above the 

 edge of the mantle, the broad and sturdy funnel being 

 perfectly free and reaching the base of the arms. Interesting 

 also is the minute size of the eyes, which are located level 

 with the edge of the mantle. They are oval and have a 

 longitudinal diameter of only 0-26 mm. Joubin has already 

 drawn attention to the small size of the eyes. 



The arms are perfectly developed, the 4th arms however 

 being very small and stumpy. The first and second pairs 

 of arms are almost equal in size, the third being some- 

 what smaller. The inner surface of all the arms is covered 

 with minute suckers, arranged in four or five longitudinal 

 rows. No traces of the tentacles are visible externally. 

 In the adult animal they may be drawn into a kind of 

 sheath and I suppose that they have already been devel- 

 oped. The upper jaws run into a point and, protruding 

 a little, push the inner lips and the buccal skin aside. 



The pigmentation of our larva is a little more 

 pronounced about the head, where densely scattered light 

 brown chromatophores with a slight touch of purple red 

 occur. The funnel and arms are entirely devoid of 

 chromatophores, and on the mantle they are also very 

 faint and scarce. The edge of the mantle shows no 

 accumulation of them, and only at the posterior end of 



the body, about the shell and around the whitish fins, 

 a small gathering of chromatophores is visible. 



As regards the more advanced larval stages (pi. I, 

 figs. 3—6) I will mention them quite shortly, as their main 

 features are similar to what has been described above. 

 The mantle still exhibits the barrel-like shape and no 

 trace of angles or indentations are visible in the edge of 

 the mantle. The shell begins to appear more distinctly 



Fig. 3. Spirula. Young 

 larva from Stat. 35. 



Fig. 4. Spirula. Advanced 

 larva from Stat. 43. 



at the posterior end of the body, and we may see 6 or 

 7 chambers, which are very sharply defined in the largest 

 larva from Stat. 42. The siphon is now and again 

 faintly visible through the chambers. The latter are always 

 covered by the thin outer skin, which in this posterior 

 region is more profusely pigmented than in the youngest 

 stage. The pigment on the edge of the mantle is be- 

 ginning to increase and the pigment on the head part 

 has expanded, covering the arm-bases. The fins have 

 grown a little, but their position has not altered per- 

 ceptibly. As the head is drawn far into the mantle, I 

 can only give prominence to the fact that the tentacles 

 are not visible in any of the more advanced larvae. The 

 arm-cluster is however very nicely displayed, and the 

 tentacles could not possibly be overlooked. A feature, 

 which is faintly noticeable even in the youngest larva, 

 has now become more prominent, for the mantle becomes 

 somewhat thickened about the chambers of the shell and 

 about the bases of the fins, even now indicating the limit 

 of the so-called ovals, which, as we know, later on appear 

 very conspicuous on the dorsal and ventral sides. 



Compared to the three larvae just described, the 

 young form from Stat. 45 (pi. II, fig. 2) exhibits a 

 marked advance in development. The dorsal mantle- 

 length is 12 mm, while in the oldest larva it is only 8 

 mm. We notice first of all that dorsal and ventral angles 

 have developed in the edge of the mantle, but rounded 



