There are numerous varieties of animals and many persons are engaged in taxonomic work. As such there is every possibility of some confusion in nomenclature. Such a confusion did occur in the past. The same name has been given to different animals and different names have been given to the same animal. Linnaeus used some rules of nomenclature and some were proposed later. The International Congress of Zoologists in 1898 appointed a permanent commission to prepare an International Code of Nomenclature and to give decisions on difficult cases. The following are some important provisions of the code.
(1) Zoological and botanical names are distinct (the same genus and species name may be used, but is not recommended for both, as animal and a plant); (2) no two genera in the Animal Kingdom may bear the same name; (3) no names are recognized prior to those included by Linnaeus in the “Systema Naturae” tenth edition, 1758; (4) scientific names must be cither Latin or latinized and preferably, printed in italics; (5) the genus name should be a single word (nominative singular) and begin with a capital letter; (6) the species’ name should be a single or compound word beginning with a small letter (usually an adjective agreeing grammatically with the genus’ name); (7) the author of a scientific name is the person who first publishers it in a generally accessible book or periodical, with a recognizable description of the animal; (8) when a new genus is proposed the type species should be indicated; (9) a family name is formed by adding I DAE to the stem of the name of the type genus, and a subfamily name by –INAE.
From an embryological point of view the vertebrates may be separated into two main divisions, the Amniota and the Anamniota, distinguished by the presence or absence of the amnion, a thin membrane that surrounds the early embryo. It occurs in reptiles, birds and mammals which together constitute the Amniota; and is absent in the fishes and amphibians which are called the Anamniota. These two divisions are also distinguished by other peculiarities. The higher forms referred to above, have an organ known as allantois, an appendage of the embryonic gut, which is lacking in the lower forms. The comparative anatomist finds many points of resemblance between the various classes of fishes on the one hand, and the Amphibia on the other, and indicates this relationship by the use of the term Ichthyopsida (“fish-like” animals). In our present classification the term Ichthyopsida in synonymous with Anamniota. The comparative anatomist further recognizes a close relationship between birds and reptiles, and puts these together under Sauropsida (“reptile-like” animals).
The following arc the generally accepted categories of classification:
The system of classification of the Chordata used in the present book is summarized in the chart given on the next page. The detailed classification of the different classes has been given after the description of the types of each class.