FISH. 151 
As Cuvier observes, the D. geometricus of Bl. and Schneid.* approaches very 
closely this species, and I can hardly think it to be distinct. Yet neither in Mr. 
Darwin’s specimen, which in all other respects agrees exactly with Schneider's 
figure, do I discern any appearance of the hexagonal meshes on the surface of 
the body. 
3. Diopon ANTENNaTUS. Cuv.? 
Diodon antennatus, Cuo. Mém. du Mus. tom. iv. p. 151. pl. 7. 
A third species of Diodon, brought home by Mr. Darwin, and taken by him at 
Bahia, in Brazil, is either the young of the D. antennatus of Cuvier, or else new ; 
but the only individual in the collection is quite small, and not more than an inch in 
length, excluding caudal. The fleshy filaments above the eyes, which, according 
to Cuvier, so peculiarly distinguish the D. antennatus, are very distinct,—but I 
see none on the sides. The ground colour would seem darker than he describes, 
so as to render the spots and markings on the upper parts not distinguishable 
from it now, if they ever existed. In spirits it appears of a nearly uniform deep 
brown red. The spines, or rather papillz, are also shorter than represented in his 
figure ; but this may be only the effect of immaturity. 
According to Mr. Darwin, the colours when recent were as follows :—‘‘ Above 
blackish brown, beneath spotted with yellow. Eye with the pupil dark blue ; iris 
yellow, mottled with black.” It is added :—** On the head four soft projections ; 
the upper ones longer, like the feelers of a snail.” 
Mr. Darwin observes, ‘‘ that the dorsal, caudal, and anal fins, in this species, 
are so close together that they act as one: these, as well as the pectorals, are in a 
continued tremulous motion even when the fish is otherwise motionless. The 
animal propels its body by using the posterior fins in the same manner as a boat 
is sculled, that is, by moving them rapidly from side to side with an oblique sur- 
face exposed to the water. The pectoral fins have great play, which is necessary 
to enable the animal to swim with its back downwards.” 
Mr. Darwin made some further observations on the habits of this species, 
which have already appeared in his “ Journal,” to which I may refer the reader. 
The tendency of them is to explain the process by which the water and air are 
absorbed, when the Diodon distends itself into a spherical form; and to show that 
the fish can swim, when floating in this state with its back downwards, which 
Cuvier doubted. He thinks that the water is taken in partly for the sake of 
regulating its specific gravity. He also notices a curious circumstance with 
respect to this species, viz., ‘‘ that it emitted from the skin of its belly, when 
handled, a most beautiful carmine red and fibrous secretion, which permanently 
stained ivory and paper.” 
* Syst. Ichth. pl. 96. + pp. 13, 14. 
