200 The Study of Animal Life part hi 



starting of course as an ovum at the level of the Protozoa, 

 has to stop as it were at the first distinctively crustacean 

 station — the Nauplius stage. After some change and 

 delay, it continues to progress, but again there is a halt and 

 a change at the Zoea station. Finally there is another 



Fig. 30a.— Life-history of Penesus; the Zoea. 



delay at the Mysis stage before the Penceus reaches its 

 destination. The crab, on the other hand, stops first at 

 the Zoea station, the lobster at the Mysis station, while the 

 crayfish though progressing very gradually like all the 

 others has — if you do not find the simile too grotesque-^a 

 through-carriage all the way. 



