OF THE EGG. 



135 



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, as sharks and vipers, 

 which, for that reason, have been named oiw -viviparous 

 animals. The eggs of the mammalia are not only developed 

 with in the mother, but become intimately united to her ; this 

 peculiar mode of development has received the name of 

 gestation. 



282. Eggs are sometimes laid one by one, as in oirds ; 

 sometimes collectively and in great number-s, as in 

 the frogs, the fishes, and most of the invertebrates. 

 The queen ant of the African termites lays 80,000 

 eggs in twenty-four hours ; and the common hair- 

 worm, (Gordius,) as many as 8,000,000 in less than 

 one day. In some instances they ar'e united in 

 cluster's by a gelatinous envelop ; in others they are -pio- 99 

 enclosed in cases or between membranous disks, 

 forming long strings, as in the eggs of the Pyrula shell, (Fig. 

 99.) The conditions under which the eggs 



of diffei'ent animals are placed, on being laid, 

 are very different. The eggs of bir'ds, and of 

 some insects, are deposited in nests constructed 

 for that purpose by the par-ent. Other animals 

 carry their eggs attached to their bodies ; 

 sometimes under the tail, as in the lobsters 

 and crabs, sometimes hanging in lar'ge bun- 

 dles on both sides of the tail, as in the Mo- 

 noculus, (Fig. 100, a.) 



2 S3. Some toads carry them on the back 

 most extraordinary, it is the male which undertakes thia 

 office. Many mollusks, the Unio for example, have theni 

 eri'j^osed between the folds of the gills dui-ing incubation. 

 Ir *he je ly fishes and polyps, they hang in clusters, eithei 



Fig. 100. 

 and, what is 



