Early in 1692, the Synopsis Methodica Animalium Quadrupedum et Serpentini Generis was finished, and published the year after. Important as were the botanical writings of Ray, his zoological works have had a more decided influence on the advancement of natural history. "Their peculiar character," says Cuvier, "consists in clearer and stricter methods than those of any of his predecessors, and applied with more constancy and precision. The divisions which he has introduced into the classes of quadrupeds and birds have been followed by the English naturalists almost to our own day; and we find very evident traces of his system of birds in Linnaeus, Brisson, Buffon, and all the authors who have treated of that class of animals." In the Synopsis of Four-footed animals and Serpents, he commences with an interesting discussion respecting the nature and faculties of animals. The definition, however, on which he proceeds is scarcely correct, or at least sufficiently distinctive:--"An animal is an animated body, endowed with sense and spontaneous motion, or rather with the faculty of feeling and moving, although it may not change place." In treating of the generation of the lower species, he discusses the subject of spontaneous or equivocal origin, the idea of which he refutes, and endeavours to prove that all animals were created at one time. The division of them into viviparous and oviparous he rejects, alleging, that all are in one sense or other oviparous. The most suitable primary division, he says, is into _blooded_ and _bloodless_, or, as we should say, red-blooded and white-blooded. The former may be divided into those which respire by _lungs_, and those which respire by _gills_. The first of these are again divided into such as have two ventricles to the heart, and such as have only one. Animals with two ventricles are viviparous, as _Quadrupeds_ and _Cetacea_, or oviparous, as _Birds_. Those having a heart furnished with a single ventricle, are the _Oviparous Quadrupeds_, and serpents. Animals that respire by gills are the true _Fishes_, not including whales. The _white_-blooded animals are divided into the larger and the smaller. The former, he says, are suitably divided by Aristotle into three kinds or orders: 1. _Mollusca_; 2. _Crustacea_; 3. _Testacea_. The smaller white-blooded animals are the _Insects_. The following table exhibits a summary of this classification, which is essentially that of Aristotle:-- _Red-blooded Animals._ Respiring by lungs, and having a heart furnished with two ventricles, viviparous, and aquatic, CETACIA. Terrestrial, QUADRUPEDS. Oviparous, BIRDS. Those having a heart with a single ventricle, OVIPAROUS QUADRUPEDS AND SERPENTS. Respiring by gills, FISHES. _White-blooded Animals._