A "Livrng Fossir 235 



dark situation the hatching can be retarded for a year; 

 but under average normal conditions, such as will be 

 assumed to be the case in this account, the period of 

 incubation is far less. 



About a week or so after the eggs are laid there 

 appears on the surface of the yolk an oval constriction 

 bearing six pairs of appendages in a row. They are the 

 merest sort of prominences and represent what will be 

 In the adult the legs. At this time, too, a faint indi- 

 cation of what is to be the abdomen can be seen toward 

 one end of the oval. The ovoid region now continues 

 to grow while the yolk gets visibly smaller until the next 

 stage of the embryo Is reached, wherein we find not 

 only an enlarged abdomen with four transverse sutures 

 denoting the formation of segments, but a distinct head 

 region on the back of which are strongly Indicated five 

 segments. This occurs about three weeks after spawn- 

 ing and by this time the cephalic legs have Increased In 

 size, are jointed, and are folded upon themselves, and 

 rudimentary gill feet have appeared on the abdomen. 

 It is now, for the first time, that the embryo shows 

 movement. The membranous shell has Increased In 

 size, leaving ample space within which little LImulus 

 continually revolves. 



A couple of days later occurs the animal's first molt. 

 Increasing growth has caused it to outlive Its old skin, 

 and cast It off within the egg, just as it will continue to 

 do In Its larval and later stages. The body Is here quite 

 plump, or globular, and Is provided with two pairs of 

 eyes, simple and compound. From now on the body 

 gradually flattens. And when, a little later, or about 

 a month and a half after spawning, the egg Is due to 



