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.
Tadpoles are aquatic vertebrates.
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