148 



ZOOLOGY 



their appearance ; then the other appendages, and the tail (Fig. 

 149). For a long time the back of the thorax is greatly dis- 

 tended by the yolk stored there, and the e,yes are huge (Fig. 

 150). During the early meltings (Fig. 151) the young lob- 

 sters undergo a terrible mortality, so that out of ten thousand 

 embryos hardly two, on the average, survive. After the fifth 



Fig. 147. — An early stage of devel- 

 opment of egg of thelolister. Ap- 

 pendages becoming bifid. Paired 

 dotted areas above indicate eyes ; 

 these are followed by the first three 

 paired appendages: antennules, an- 

 tenn£e, and mandibles. Below in 

 the middle line is the forming tail ; 

 above is the mouth. After Herrick. 



Fig. 148. — Surface view of egg nau- 

 phius. Antennee show beginning of 

 segmentation ; mandibles and max- 

 illae seen on each side of the abdo- 

 men. Embryo 16-18 days old. 

 X 25. From Herrick. 



or sixth molt the little lobsters sink to the bottom, and then 

 begin their journey shoreward. From this time until they are 

 about four inches long, only verj^ few individuals have ever 

 been seen. This is due, it is said, to the fact that they hide 

 deep down among the rocks, where the}^ cannot be dredged. 

 When ihej are four inches long or so, they become bolder, 

 leave the rocks, and, like the adults, make burrows for them- 

 selves in the sand or under stones. 



Development of Crayfish. — The crayfish develops simi- 



