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 larve (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, « 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.” 
