OF THE EGG. 105 



279. Ovulation. Having attained a certain degree of 

 maturity, which varies in different classes, the eggs leave 

 the ovary. This is called ovulation. It must not be con- 

 founded with the laying of the eggs, which is the subsequent 

 expulsion of them from the abdominal cavity, either imme- 

 diately, or through a particular canal, the oviduct. Ovula- 

 tion takes place at certain seasons of the year, and never 

 before the animal has reached a particular age, which com- 

 monly coincides with its full growth. In a majority of spe- 

 cies, ovulation is repeated for a number of years consecu- 

 tively, generally in the spring, and frequently several times 

 a year. In others, on the contrary, it occurs but once 

 during life, at the period of maturity, and the animal 

 soon afterwards dies. Thus the butterfly dies shortly after 

 having laid her eggs. 



280. The period of ovulation is one of no less interest to 

 the zoologist than to the physiologist, since the peculiar 

 characteristics of each species are then most clearly 

 marked. Ovulation is to animals what flowering is to 

 plants ; and indeed, few phenomena are more interesting to 

 the student of nature than those exhibited by animals at the 

 pairing season. Then their physiognomy is the most 

 animated, their song the most melodious, and their attire the 

 most brilliant. Some birds appear so different at this time, 

 that zoologists are always careful to indicate whether or not 

 a bird is represented at the breeding season. Similar differ- 

 ences occur also among fishes and other animals, whose 

 colors are then much brighter. 



281. Laying. After leaving the ovary, the eggs are 

 either discharged from the animal, that is, laid ; or they 

 continue their development within the parent animal, as is 

 the case in some fishes and reptiles, which for that reason 

 have been named ovo -viviparous animals. The eggs of the 

 mammalia are not only developed within the mother, but 



