32 MANUAL OF ZOOLOGY, 



again, constitute one of many orders of quadrupeds, which are distinguished 

 by suckling their young and by other common characters, and which 

 collectively constitute the "class" Mammalia. Finally, the Mammalia 

 are united with the classes of the Birds, Reptiles, Amphibians, and Fishes 

 to constitute the great primary division or " sub-kingdom " of Vertebrata 

 or " Vertebrate animals ; " since all these classes agree with one another in 

 certain fundamental points of structure. 



Condensing the above, the name of Cants familiaris, as applied to the 

 Dog, implies a large amount of information as to the precise zoological 

 position and affinities of the animal. Its title, namely, if expressed in full, 

 would indicate its systematic place to be as follows : 



Sub-kingdom, VERTEBRATA. 



Class, Mammalia. 

 Order, Carnivora. 

 Family, Canida. 

 Genus, Cants. 

 Species, Cam's familiaris. 



ii. REPRODUCTION. 



Reproduction is the process whereby new individuals are 

 generated and the perpetuation of the species insured. The 

 methods in which this end may be attained exhibit a good 

 deal of diversity, but they may be all considered under two 

 heads. 



I. Sexual Reproduction. This consists essentially in the 

 production of two distinct elements, a germ-cell or ovum, and 

 a sperm -cell or spermatozoid, by the contact of which the 

 ovum now said to be " fecundated " is enabled to develop 

 itself into a new individual. As a rule, the germ-cell is pro- 

 duced by one individual (female) and the spermatic element 

 by another (male) ; in which case the sexes are said to be dis- 

 tinct, and the species is said to be "dioecious." In other 

 cases the same individual has the power of producing both the 

 essential elements of reproduction ; in which case the sexes 

 are said to be united, and the individaal is said to be " her- 

 maphrodite," " androgynous," or " monoecious." In the case 

 of hermaphrodite animals, however, self- fecundation contrary 

 to what might have been expected rarely constitutes the re- 

 productive process ; and, as a rule, the reciprocal union of two 

 such individuals is necessary for the production of young. 

 Even amongst hermaphrodite plants, where self-fecundation 

 may, and certainly does, occur, provisions seem to exist by 

 which perpetual self-fertilisation is prevented, and the influence 

 of another individual secured at intervals.* Amongst the 



* It seems to have been established as a strong probability by Darwin, 

 Hildebrandt, and Delpino, that in the great majority of plants self-fecunda- 



