This structure is of a most unexpected character. The creature has rows of gills on either side of its head, and with these it breathes while it is in the water. The swimming-bladder, however, is modified so as to act as a substitute for a lung. A branch of the artery which supplies the gills is diverted to the swimming-bladder, and as there is a communication between the interior of the swimming-bladder and the external air, the creature is able to aerate its blood sufficiently to sustain life until it can assume its normal fish life.
I may here mention that these African and American Lepidosirens, together with the Australian Ceratodus are especially interesting as being one only living survivor of a vast family which in bygone ages were extremely numerous.
The Ceratodus is a comparatively new discovery, and came on naturalists by surprise. Until lately the only known examples of this fish were to be found in the earlier secondary rocks, and when it was announced that living specimens had been found, the discovery could hardly be believed. However, there the Ceratodus is. It looks like a resuscitated fossil, and is to our known fishes what the tree-fern is to our present vegetation.
There is another interesting point about this object, showing how Estivation is connected with Scripture.
The mud of which the cocoon is made is the same as that which the Israelites, while in captivity, were forced to make into bricks. It is so tenacious, that although merely dried by the Egyptian sun, it is so hard that I was obliged to employ mallet, chisel, saw, and butcher’s knife, while making the necessary sections.
Occasionally the difficulty was increased by vegetable fibers which had become mixed with it, and which bound it together just as the cow-hairs bind builder’s plaster when honestly made. The Egyptians mixed straw with the clay of which their bricks were made, so as to strengthen it, and in order to secure a supply of such straw they did not reap their corn near the ground as we do, but cut off the ears close to the stem, leaving the stubble to be cut separately. The reader will remember that one of the grievances of the captives was, that instead of being supplied with straw, as formerly, they had to cut and fetch the stubble for themselves, and yet were forced to deliver the same number of bricks daily.
So here is my lump of Nile mud acting as a link representing nearly four thousand years between the Christian world of the present day, and the long-perished Egyptian dynasty of the Pharaohs.
Now we will pass to the opposite side of the world.
In tropical America, as in tropical Africa, the rivers are dried up in the summer, and the mud which forms their banks and bed is baked as hard as that of the Nile and other African rivers. Many of these rivers are inhabited by a fish (Callicthys) popularly called the Hassar, or Hardback. The latter name is given to it in consequence of two rows of hard, narrow scales on each side of the body. There are four long, flexible tentacles on the upper lip. It is not nearly so large as the Lepidosiren, seldom exceeding eight inches in length. Its color is greenish brown.
Unlike the Lepidosiren, which can not travel on dry ground, the Hassar is as good a walker as the Climbing Perch, a fish which not only leaves the water and traverses dry land, but can ascend the trunk of trees. All rivers have some portions deeper than others, “holes” as we call them in our rivers at home. So, when the process of drying up is nearly completed, the river is converted into a ravine along which “holes” or pools are seen at irregular distances.