The creek flowed over a succession of rock ledges and formed pools at the edge where tadpoles swam.
After comparing the salamanders and the perenni-branchiate Urodela with the tadpoles and the frogs, and enunciating the law that the more highly any animal is organized the more quickly does it pass through the lower stages, Meckel goes on to say: " From these lowest Vertebrata to the highest, and to the highest forms among these, the comparison between the embryonic conditions of the higher animals and the adult states of the lower can be more completely and thoroughly instituted than if the survey is extended to the Invertebrata, inasmuch as the latter are in many respects constructed upon an altogether too dissimilar type; indeed they often differ from one another far more than the lowest vertebrate does from the highest mammal; yet the following pages will show that the comparison may be also extended to them with interest.
In describing tadpoles, the term "body" is therefore used as meaning head and body.
This orifice is the spiraculum, which is lateral, on the left side of the body, in most tadpoles, but median, on the breast or belly, in those of the Discoglossidae and of some of the Engystomatidae.
In addition to these lines, all tadpoles show more or less distinctly a small whitish gland in the middle of the head between the eyes, the so-called frontal gland or pineal gland, which in early stages is connected with the brain.
The above description applies to all European and North American tadpoles, and to the great majority of those known from the tropics.
In some Indian and Malay Engystomatids of the genera Callula and Microhyla, the tadpoles are remarkably transparent, and differ markedly in the structure of the buccal apparatus.
In the Aglossal Xenopus, the tadpoles are likewise devoid of circular lip, horny teeth, and beak, and they are further remarkable in the following respects: There is a long tentacle or barbel on each side of the mouth, which appears to represent the "balancer" of Urodele larvae; the spiraculum is paired, one on each side; the fore limbs develop externally, like the hind limbs.
Some tadpoles reach a very great size.
Among European forms, some tadpoles of Pelobates attain a length of seven inches, the body being of the size of a hen's egg.
Boulenger, "A Synopsis of the Tadpoles of the European Batrachians," P.Z.S., 1891, p. 593; F.
The tadpoles grow to a large size considering that of the adult, the body equalling in size a sparrow's or even a small pigeon's egg, and they often remain more than a year in that condition.
The atrium is thus analogous to the opercular cavity of fishes and tadpoles, and, as stated above, remains in communication with the exterior by means of the atriopore.
Once there were eleven tadpoles in a glass globe set in a window full of plants.
It was great fun to plunge my hand into the bowl and feel the tadpoles frisk about, and to let them slip and slide between my fingers.
I love to see that Nature is so rife with life that myriads can be afforded to be sacrificed and suffered to prey on one another; that tender organizations can be so serenely squashed out of existence like pulp--tadpoles which herons gobble up, and tortoises and toads run over in the road; and that sometimes it has rained flesh and blood!