110 ANIMAL FORMS 



many internal rods of cells, provided with an abundant 

 nerve-supply. These latter elements may perhaps repre- 

 sent simple eyes grouped together to form the compound 

 one ; and it appears possible that each element may form 

 a complete image of an object, as each of our eyes is known 

 to do. On the other hand, many hold that the complete 

 eye forms only one image, a mosaic, each element con- 

 tributing its share. 



108. Growth and development. As we have seen, the 

 simpler Crustacea hatch as minute larvae (Fig. 56), and dur- 

 ing their growth to the adult condition are especially sub- 

 ject to the attacks of multitudes of hungry enemies. In 

 the higher forms, such as the crabs, some of these early 

 transformations take place while the young are still within 

 the egg and attached to the parent. Accordingly, the little 

 ones are fairly similar to their parents, and their later his- 

 tory is very well exemplified by the lobster. 



The eggs of the lobster are most frequently hatched in 

 the summer months, usually July, after they have been 

 carried by the parent for upward of a year. The young, 

 about a third of an inch in length, at once disperse, undergo 

 four or five moults during the next month, then, ceasing 

 their swimming habits, settle to the bottom among the 

 rocks. At this time, twice their original size, they closely 

 resemble their parents, and their further development is 

 largely an increase in size. " The growth of the lobster, 

 and of every arthropod, apparently takes place, from in- 

 fancy to old age, by a series of stages characterized by the 

 growth of a new shell under the old, by the shedding of 

 the outgrown old shell, a sudden increase in size, and the 

 gradual hardening of the shell newly formed. Not only is 

 the external skeleton cast off in the moult and the linings 

 of the masticatory stomach, the esophagus, and intestine, 

 but also the internal skeleton, which consists for the most 

 part of a complicated linkwork of hard tendons to which 

 muscles are attached." 



