INHERITANCE IN THE "WALKING-STICK. 



243 



Finally, is this adjustment between the structure of the femora 

 and head due to the position of the insect when enclosed within 

 the inelastic egg shell ? If the first legs were folded forward against 

 the head the pressure during embryonic life might easily be suf- 

 ficient to mold the femur curve into pattern for the head. Twenty 

 eggs containing embryos at various stages shortly preceding 

 hatching were dissected with this question in view. The ellipti- 

 cal egg shell is of a rigid chitinous material with a circular oper- 

 culum at one end and a hilum-like scar on one side to which the 



FIG. 2. An unhatched Aplopus with its egg membranes dissected away showing 

 its folded position. The femora of the three right legs are marked with roman 

 numerals and the tarsal ends of the same legs are indicated by figures. The part of 

 the first femur which in later life fits against the head is shown between the points 

 x-x, it is not molded against the head in the egg. A, antennae ; , compound eye ; 

 M, mandible. 



inner egg membrane is attached. The size of the egg ranges 

 from 2 mm. in narrow diameter by 4 mm. in long diameter to 3 

 mm. by 4.5 mm. The length of the walking-stick on hatching 

 is from 17 mm. to 23 mm. measured from the tip of abdomen to 

 tip of the first pair of legs when extended forward, or from tip 

 of head to tip of tail 9.5 mm. to 13 mm. The embryo within 

 the egg is, therefore, necessarily much folded and bent. 



