,c8 THE RABBIT. PHYLUM CHORDATA 



contents takes place, and in this way the nutrition and respira- 

 tion of the young are provided for until birth, which takes place 

 at the end of a month from fertilisation. Animals in which, 

 as in the rabbit, a great part of development takes place within 

 the body of the mother, so that the young when they are born 

 are beyond the need of a shell or similar covering, are said to 

 be viviparous. The wild rabbit may breed in any month of the 

 year, but the main season is from January to June, when almost 

 all females become pregnant at every oestrus, so that there may 

 be about eight litters a year. More than half of the litters are 

 never born, but are completely resorbed into the uterus ; this 

 happens more often with the larger litters, so that the most 

 productive Utter size is the average of five to six. The animals are 

 promiscuous and able to breed at six months. Before producing 

 her young the female makes a nest of leaves, and fur from her 

 own body. The life of a rabbit may be seven or eight years. 



NERVOUS SYSTEM 



The actions of the body are for the most part co-ordinated 

 by the nervous system. In the vertebrate this has two main 

 parts — the cerebrospinal system, connected with the organs of 

 sense and the voluntary muscles ; and the autonomic system, 

 connected principally with the viscera and blood vessels. The 

 cerebrospinal system comprises the central nervous system or 

 cerebrospinal axis, composed of the brain and the spinal cord, 

 and the peripheral nervous system, containing the cerebrospinal 

 nerves and certain knots of nerve cells upon them, known as 

 their ganglia. The cerebrospinal nerves are usually twelve pairs 

 of cranial nerves arising from the brain, and a variable number of 

 spinal autonomic nerves. The system also consists of nerves and 

 ganglia. Nerves are made up of nerve fibres, and these are either 

 afferent, conveying impulses from sense organs to the central 

 nervous system, or efferent, taking impulses out to muscles and 

 glands and other effector organs which do the work of the body. 

 The central nervous system has an inner grey matter, consisting 

 chiefly of nerve cells, and an outer white matter, mainly of nerve 

 fibres which run up and down the spine. The detailed structure 

 of fibres and cells is shown on pp. 511-513. 



The spinal cord runs the whole length of the neck and body, 

 within the neural canal of the vertebrae ; at its front end it is 



