among birds and other advanced vertebrates a partial reversion to the earlier habit not infrequently takes place.  With doves, for example, the cock and hen birds sit equally on the eggs, taking turns about at the nest; and as for the ostriches, the male bird there does most of the incubation, for he accepts the whole of the night duty, and also assists at intervals during the daytime.  There are numerous other cases where the father bird shares the tasks of the nursery at least equally with the mother.  I will glance first, however, at one of the rare exceptions among fish where the main duty does not devolve on the devoted father.

[Illustration:  NO. 4.  FEMALE TUBE-MOUTH.]

In No. 4 we have an illustration of the tube-mouth or Solenostoma, one of the two known kinds of fish in which the female shows a sense of her position as a mother.  The tube-mouth, as you can see at a glance, is a close relation of our old friend the seahorse, whose disguised and undisguised forms in Australia and the Mediterranean we have already observed when dealing with the question of animal masqueraders.  Solenostoma is a native of the Indian Ocean, from Zanzibar to China.  In the male, the lower pair of fins are separate, as is usual among fish; but in the female, represented in the accompanying sketch, they are lightly joined at the edge, so as to form a sort of pouch like a kangaroo’s, in which the eggs are deposited after being laid, and thus carried about in the mother’s safe keeping.  No. 5 shows the arrangement of this pouch in detail, with the eggs inside it.  The mother Solenostoma not only takes charge of the spawn while it is hatching in this receptacle, but also looks after the young fry, like the father stickleback, till they are of an age to go off on their own account in quest of adventures.  The most frequent adventure that happens to them on the way is, of course, being eaten.

[Illustration:  NO. 5.  POUCH OF TUBE-MOUTH.]

[Illustration:  NO. 6.  PIPE-FISH.]

The common English pipe-fish is a good example of the other and much more usual case in which the father alone is actuated by a proper sense of parental responsibility.  The pipe-fish, indeed, might almost be described as a pure and blameless rate-payer.  No. 6 shows you the outer form of this familiar creature, whom you will recognize at a glance as still more nearly allied to the sea-horses than even the tube-mouth.  Pipe-fishes are timid and skulking creatures.  Like their horse-headed relations, they lurk for the most part among sea-weed for protection, and being but poor swimmers, never venture far from the covering shelter of their native thicket.  But the curious part of them is that in this family the father fish is provided with a pouch even more perfect than that of the female tube-mouth, and that he himself, not his mate takes sole charge of the young, incubates them in his sack, and escorts them about for some time after hatching.  The pouch, which is more