REPORT ON SPIRULA. 
11 
structure (PI. VI. figs. 14 and 15) are made from the Challenger specimen ; Professor 
Giard’s specimen showed the same conformation except that the papilla in it was less 
voluminous. 
The base of the conical papilla is formed by a lenticular body of fibrous tissue (PL VI. 
fig- 14, l ) presenting nuclei among the fibres (PI. VI. fig. 16). A layer of bright glassy¬ 
looking substance (PL VI. figs. 14 and 15, m), resembling the elastic tissue of Vertebrates, 
covers the aboral surface of the lenticular body, and extends over the whole central mass 
of the papilla, which it thus bounds ; this layer appears to become thin near the 
, summit of the papilla, but it must be remembered that in the two individuals studied 
this summit was very much damaged. 
Finally, a layer of fibres, very probably muscular, radiates, in front of the lenticular 
body, from the centre to the periphery (PL VI. figs. 14 and 15, r). 
Fig. G.—Embryo of Loligo, dorsal 
view; magnified, i, arms; ii, 
mantle; iii, fins ; iv, eye. 
Fig. H.—Embryo of Sepia, dorsal view : 
magnified, i, arms; ii, mouth ; iii. 
eye ; iv, fin. 
Fig. I.—Aboral view of Spirula reti¬ 
culata ; x 2. i, left fin ; ii, aboral 
fossa ; iii, ventral external part of 
the shell; iv, terminal disk; v, 
mantle ; vi, dorsal external part 
of the shell. 
Function of the Fossa .—The conformation of this organ has remained unknown up 
to this time, though various authors have expressed the opinion that it is an adhesive 
apparatus, founded on a supposed observation of Rumphius, according to whom “ Spirula 
attaches itself to rocks by its terminal disk.” Now Rumphius makes no mention of the 
terminal disk nor of the fossa (op. cit., p. 68), nor indeed of any other external part of 
Spirula. It is certain, as I have already pointed out, that if he saw any parts they were 
only very unimportant fragments. According to his obscure text one must conclude that 
he believed that Spirula fixed itself to rocks by the mouth ; he knew the siphuncle and 
the immediately adjacent parts, contained in the last chamber of the shell, and he supposed 
that the siphuncle traversed the whole animal, which fixed itself by the oral extremity 
