THE MECHANISM IN THE HATCHING OF THE WALK- 

 ING STICK, DIAPHEROMERA FEMORATA SAY. 



By Henry P. Severin, Ph. D., Professor of Zoology and Entomology, 



College of Hawaii, and Harry C. Severin. M. A., Professor of 



Entomology, South Dakota State College of Agriculture 



and Mechanic Arts. 



(WITH PLATE XIV.) 



In the Phasmidae, Mantidae, Blattidae and Acridiidae, the 

 cervical ampulla is said to play an inportant role in the process 

 of molting, and in some Orthoptera, also in the process of hatch- 

 ing. This ampulla, consisting of a soft membrane joining the 

 head dorsally to the prothorax, can be transformed by the afflux 

 of blood into a greatly swollen pouch, which then projects out 

 immediately behind the head. 



The process of hatching of various Orthoptera has been 

 studied by a number of entomologists. Riley (7) does not men- 

 tion the cervical ampulla while describing the phenomenon of 

 hatching in the Rocky Mountain Locust, for he writes as fol- 

 lows : "The hatching consists of a continued series of undulating 

 contractions and expansions of the several joints of the body, 

 and with this motion there is slight but constant friction of the 

 tips of the jaws and of the sharp tips of the hind tibial spines, 

 as also of the tarsal claws of all the legs against the shell, which 

 eventually weakens and finally gives away. It then easily 

 splits up to the eyes or beyond, by the swelling of the head." 



Packard (5) objects to Riley's account of the supposed 

 action of the jaws and spines and believes that "the egg-shell 

 is without doubt burst open by the puffing out or expansion 

 of the membrane connecting the head and prothorax, just as the 

 common house-fly or flesh-fly bursts off the end of its pupa- 

 case by the puffing out of the front of the head." 



Kunckel d'Herculais (3 and 4) gives the following account 

 of the physiological mechanism in the hatching of the Acridii- 

 dae: " Les Acridiens rompent la coque de l'oeuf, * * * par la pres- 

 sion exercee a l'aide de la membrane unissant dorsalement la 

 tete au prothorax que se transforme par afflux de sang en une 

 ampoule cervicale." 



In Diapheromera femorata the mechanism, which ruptures 

 the various membranes and springs off the operculum when the 

 walking-stick is about to emerge from the egg, cannot be ob- 

 served in action on account of the hard, thick, opaque chorion. 

 If the operculum is carefully removed from an egg shortly 



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