OF THE EGG. 275 



in nests constructed for that purpose by the parent. Other 

 animals carry their eggs attached to their bodies ; sometimes 

 under the tail, as in the lobsters and crabs, sometimes hanging 

 in larjje bundles on both sides of the tail, as in the Monoculus 

 (fig. 286, a). 



440*. Some toads carry them on the back, and, what is 

 most extraordinary, it is the male which undertakes this office. 

 Many mollusca, the Unio for example, have them enclosed be- 

 tween the folds of the gills during incubation. In the medusae 

 and polyps, they hang in clusters either outside or inside, at 

 the bottom of the cavity of the body. Some insects, such as 

 the gad-flies, deposit their eggs on other animals. Finally, 

 many abandon their eggs to the elements, taking no further 

 care of them after they have been laid ; such is the case with 

 most fishes, some insects, and many mollusca. As a general 

 rule, it may be said that animals take the more care of their 

 eggs and brood, as they occupy a higher rank in their respective 

 classes. 



441. The development of the embryo does not always 

 take place immediately after the egg is laid. A considerable 

 time even may elapse before it commences. Thus, the first 

 eggs laid by the hen do not begin to develop until the whole 

 number which is to constitute the brood is deposited. The 

 eggs of most butterflies, and of insects in general, are laid in 

 autumn, in temperate climates, and remain unchanged until 

 the following spring. During this time the principle of life 

 in the egg is not extinct, but is simply inactive, or in a latent 

 state. This tenacity of life is displayed in a still more striking 

 manner in plants. Their seeds, which are equivalent to eggs, 

 preserve for years, and even for ages, the power of germinating. 

 Thus, there are some well-authenticated cases in which wheat 

 taken from the ancient catacombs of Egypt has sprouted and 

 grown. 



442. A certain degree of warmth is requisite* for the 

 hatching of eggs. Those of birds, especially, require to be 

 submitted for a certain length of time to a uniform tempera- 

 ture, corresponding to the natural heat of the future chicken ; 

 and which is naturally supplied by the body of the parent. In 

 other words, incubation is necessary for their growth. In- 

 cubation, however, is not a purely vital phenomenon, but may 

 be readily imitated by artificial means. Some birds of warm 



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