Belonging to the same group of fishes is the fighting fish, Bella pugnax, whose breeding habits are interestingly described by Waite (1904). This fish is so named because it is bred and trained for fighting by the Siamese. Waite describes in detail its breeding habits, but we are interested here only in its collecting the scattered eggs in its mouth and transporting them to the nest. Waite also (1905) finds a similar habit practiced by the paradise fish, Polyacanthus opercularis, the other Macropodes being probably cultivated varie ties of this fish. Here again the female assists the male in collecting the eggs and carrying them to the nest made of foam. In one case the fish retained the eggs in the mouth for the space of one minute, this being a matter worthy of particular note in this connection.
And last of all for the osphromenid fishes, we find an identical habit described in Zernecke's Leitfaden for 1907 in the male of Macropodus viridi-auratus, which is a cultivated variety of Polya canthus opercularis.
There must now be noted certain isolated instances of mouth carrying by fishes, the last of which brings us close up to the gaff topsail. In the year 1874 Carbonnier described the breeding habits of a fish exotic in France (having been imported from North America), which he called Fundula cyprinodonta. Dr. Theodore Gill, however, declared it to have been Umbra pygmea (Science, Dec. 21, 1906). Carbonnier notes that after the extrusion and fertilization of the eggs "the female sucked them into her mouth and appeared to take great pleasure in rolling them around therein, nevertheless she replaced them" whence she had taken them. "When the eggs are found to to be a little scattered, it is clear that the female is no longer their only shield and protector, for the males also suck them into their mouths and pass them from one to another. At this time, the move ments which they execute with their fins denote great satisfaction. As they replace the eggs without alteration and without damage, the female shows no air of inquietude; nevertheless at times she turns her head and makes pretense of driving them away." During hatching the female solicitously guards the eggs and carefully removes with her mouth all bad eggs.
One other instance, and we are ready to come to the catfishes. The miller's thumb, Cott= gobio, lays adhesive eggs which are guarded by the male. Of it Thomas Peek says (1869): "On the occasion of one of the small fish emerging from its egg, the parent chased it to the bottom of the tank, and, taking it gently in his mouth, replaced it in the cluster." Further search through the literature would probably reveal other instances of this habit, but incidents enough have been given to make it clear that mouth transportation, as well as gestation, is not alto gether unusual. However, similar habits are now to be described in members of the very family of catfishes themselves.
At the 1902 meeting of the American Association for the Advance ment of Science, Dr. H. M. Smith, the present United States Commissioner of Fisheries, presented an interesting paper upon the breeding habits of the common yellow catfish, Amieurus nebulosus. The particular point in this paper which is of interest just here may be quoted as follows: "The most striking act in the care of the eggs was the sucking of the egg masses into the mouth and the blowing of them out with some force. The . . . . mouthing operations were continued with the fry until they swam freely, when the care of the young may be said to have ceased The predaceous feeding habits of the old fish gradually overcame the parental instinct; the tendency to suck the fry into their mouths continued, and the inclination to spit them out diminished, so that the number of young dwindled daily."
The above is from the abstract of Smith's paper published in Sci ence (Feb. 13, 1903). The complete account is to be found in a paper by Smith and Huron (1903), published in the Bulletin of the United States Fish Commission for 1902. In this they say: "The most striking act in the care of the eggs was the sucking of the egg masses into the mouth and the blowing of them out, this being repeated sev eral times with each cluster before another lot was treated . . . .
"The very young fry were also taken into the mouths of the parents and blown out; especially those which became separated from the main lot and were found in sand and sediment. The old fish would take a mouthful of fry and foreign particles, retain them for a moment, and expel them with some force. After the young began to swim and became scattered, the parents continued to suck them in, and, as subsequently developed, did not always blow them out . . . .
"The fry which were left with their parents continued healthy, but their number steadily decreased. There being no way for them to escape; .. . it was suspected that the old fish were eating their young .. . . They were kept under close observation during the day, and were seen to be fond of mouth ing the fry, more especially the weaker ones . . . . They were frequently seen to follow leisurely a fry, suck it into their mouth, retain it for a while, and then expel it, sometimes only to capture it again. There was no active pursuit of the fry, and the tendency seemed to be to spit them out. In one or two instances, however, it appeared that fry taken into the mouth were not liberated, the feeding instinct becoming paramount to the paternal in stinct. After all the fry which had been left with their parents had disappeared, in about 6 weeks after hatching, 18 fry were placed in the aquarium one even ing, and only 2 of these survived on the following morning." It seems hardly necessary to argue the question as to the origin of the habit of oral gestation after the presentation of the facts above given. In the mind of the present writer there is no doubt that having begun by taking up the eggs and young for purposes of trans portation, the fish have presently learned to retain them for longer and longer periods of time; we have a record of at least one minute's retention; and as the fish which retain their young even for short spaces of time and transport them to safer localities are more likely to leave descendants, through the action of natural selection, these fish and this habit will be perpetuated. Hence we may conjecture that as time has gone on the habit of retention has become more and more fixed until finally oral gestation has become an established habit.
Nor does the matter of abstinence from food offer any difficulty just here. It is known that many fishes which guard their nests do not feed while on such duty, and this is particularly true of the stickle backs and gouramies. So this fits in well with the conjectural expla nation just offered.
To the present writer all the data available lead to the conclusion just set forth, and to it he gives his full adherence.