OPHIDIOIDS. 
599 
into the respiratory tree, until only the forepart remains 
outside. The fish now entirely enters the body of the 
sea-cucumber by means of a few powerful, undulating 
movements. Now and then it peeps out to breathe, to 
seize some small crustacean that has come too near, 
or to evacuate the contents of its intestine through 
the vent, which is situated far forward. The fish must 
also, in all probability, leave its place of refuge and 
lead an independent life during the spawning-season. 
After the first fish a second, a third, or even a seventh 
may take up its abode in the same sea-cucumber. One 
Fierasfer seems generally to do no harm to the sea- 
cucumber; but if several come, it dies after ejecting 
its entrails, and the fish peep out from the empty skin. 
Thus, the Fierasfer lives originally in the ramified 
breathing duct (respiratory tree) of the sea-cucumber; 
but by the bursting of the walls of this duct it easily 
gains a, passage into the large cavity of the body, 
where it is frequently found. Some species of the ge- 
nus lead a similar life in the body cavity of the Indian 
t repangs, and in all probability gain entrance in the 
same manner; but the Fierasfers that live within the 
body of the large starfishes (genus Culcita), must cer- 
tainly pass through the mouth, for in these animals 
there is no anal aperture (cloaca) to admit of the pas- 
sage of any fish. 
Even though these fishes may derive some nourish- 
ment from the fluids in the body of the sea-cucumber 
in which they live, still they are no true parasites, and 
seek their food chiefly outside, thus being frequently 
found swimming freely about. The case may be 
different in the other genus of this subfamily, Enclie- 
Hophis, which is a native of the waters round the Phi- 
lippine Islands, and whose parasitic nature seems to be 
more pronounced and to have involved the loss not 
only of the ventral, but also of the pectoral fins. 
From the Gulf of Panama, on the west coast of 
Central America*, Putnam has described a species, Fie- 
rasfer dubius, that hospitates in pearl-mussels, be- 
tween the mantle and the shell. Here it leads a life 
so quiet and inoffensive that the mussel sometimes 
succeeds in enveloping it in a layer of nacre. 
The weak sight possessed by these fishes, at least 
by daylight, is compensated by a special development of 
the 'senses of touch and hearing. The system of the 
lateral line (fig. 144) includes large passages on the 
head, from the snout round the eyes (the suborbital 
and supraorbital branches), along the forehead and the 
top of the head on each side to the temples, and from 
the under surface of the lower jaw, along the margin 
of the preoperculum, to the same spot, where the lateral 
line proper begins. The two lateral halves of the sys- 
tem are united by transverse canals between the eyes 
and between the temples. The sensory organs lie in 
large numbers along these canals as well as in a row 
along each side of the back and in another denser row 
along each side of the base of the anal fin. The laby- 
rinth is remarkable for its comparatively large otoliths. 
The powers of hearing are probably strengthened — 
and sounds perhaps produced, though we have no ob- 
servations on this head — principally by the connexion 
Fig. 144. Cephalic system of the lateral line (“muciferous canals’’) 
in Fierasfer cleutatus. A. from above; B. from the left. 
After Emery. 
(probably common to all the Ophidioids) between the 
air-bladder, the first vertebrae, and the base of the 
occiput. In the Cods we have seen an internal con- 
nexion between the air-bladder and the transverse 
processes of the middle and posterior abdominal verte- 
brae. Here this connexion is removed farther forward; 
and the first four (or, as in Fierasfer dentatus, only 
the first three) vertebrae with their ribs are modified 
accordingly. The first vertebra is as usual close! v 
united to the occipital bone, the second is shortened. 
The first two pairs of ribs retain a. greater or less amount 
of mobility, the third (and in Fierasfer acus even the 
fourth) pair coalesces with the body of the vertebra 
like ordinary transverse processes. In Fierasfer acits 
the third pair is so much enlarged that it coalesces 
a According to Putnam (Proc. Soc. Nat. Hist. Boston, vol. XVI (1874), p. 343) the same species inhabits Holothurians on the east 
coast of Central America, in Florida Bay. 
Scandinavian Fishes. 
76 
