METAMORPHOSES OF ANIMALS. 



145 



mollusks are truly crustaceans ; and this result of modern 

 researches is confirmed in the clearest manner by the study 

 of their transformations. The following figures represent 

 the different phases of the duck-barnacle (Anatifa). 



d Fig. 148. e 



372. The Anatifa, like all Crustacea, is reproduced by 

 eggs, specimens of which, magnified ninety diameters, are 

 represented in figure 148, a. From these eggs little ani- 

 mals issue which have not the slightest resemblance to the 

 parent. They have an elongated form (Z>), a pair of ten- 

 tacles, and four legs, with which they swim freely in the 

 water. 



373. Their freedom, however, is of but short duration. 

 The little animal soon attaches itself by means of its tenta- 

 cles, having previously become covered with a transparent 

 shell, through which the outlines of the body, and also a very 

 distinct eye, are easily distinguished (Fig. 148, c). Figure 

 148, d, shows the animal taken out of its shell. It is plainly 

 seen that the anterior portion has become considerably 

 enlarged. Subsequently, the shell becomes completed, 

 and the animal casts its skin, losing with it both its eyes 

 and its tentacles. On the other hand, a thick membrane 

 lines the interior of the shell, which pushes out and forms 

 astern (e), by means of which the animal fixes itself to 



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