Medical Officers of the Army of India.

53

      Günther, Ann. Mag. Nat. Hist. (4), XVII, 1876, p. 403. and Introduction to the
Study of Fishes, p. 162.

      Lidth de Jeude, Notes Leyden Mus. IX, 1887, p. 137.

      Surbeck, Zool. Anzeiger, April 1900, p. 229.

      4. On Certain Secondary Sexual Characters in Certain Bony Fishes.

      Darwin in the Descent of Man (2nd ed., pages 330-347) has collected
numerous observations on this subject. To the cases, quoted by him, in which the
male is more brilliantly coloured or highly ornamented than the female, probably
with the object of attracting the female, the " Investigator" is able to add the
following:—

      In the Pleuronectoids Arnoglossus macrolophus and Brachypleura xantho-
sticta the first few rays of the dorsal fin are, in the adult male alone, enormously
lengthened to form an elegant erectile crest. In Arnoglossus macrolophus the
longest of these rays are more than half, and in Brachypleura xanthosticta they
are nearly half the total length of the body.

      In the Ophidioid Neobythites pterotus the male alone has the rays of the
pectoral fins much prolonged, with spathulate tips, the corresponding fins of the
female being of the ordinary length and form. As however this species is an
inhabitant of the dark or gloomy depths, it is probable that the curious fin-rays of
the male, though undoubtedly ornamental to our eyes, are òrgans of touch useful
for detecting the presence of the female.

      In the Pleuronectoid Rhomboidichthys asureus the male alone has a short
horizontally-directed horn on its snout, and is ornamented on the broad space in
front of the eyes with two rows of azure blue spots of extraordinary brilliance.

      In Rhomboidichthys valde-rostratus the male is armed and ornamented in
the same way, but as the female is unknown, we cannot say whether or not this is
a sexual character.

      In the Gobioid Callionymus carebares the sexes differ in colouration only,
not in size of body or in length of fins. But in this species, contrary to the usual
state of things—though parallel cases are known in certain birds—it is the female,
and not the male, that is the brighter.

      5. A Case of Pairing in an Eel.

      In November and December eels, of the common reef-haunting species
Murœna pseudothyrsoidea, are sometimes found in swarms in the tidal pools of the
Laccadives and Andamans. Their behaviour is then very aggressive, and if dis-
turbed, instead of making off, they await the enemy with open mouth and may
even begin the attack. Once, when collecting among the pools of Betra Par reef
in the Laccadives, I was glad, on account of these eels, to be wearing thick boots.