548 R. fV. Hegner 



shaken. Some experiments by Morgan ('04, p. 96) upon the 

 toad's egg seem to show that agitation hastens the development. 

 Whitney ('06, p. 47) finds that "mechanical shocks and vibrations 

 are not effective in accelerating the early segmentation of the 

 fertilized eggs of Arbacia, Asterias, Fundulus and Ctenolabrus." 

 The development of the eggs of Hydrophilus aterrimus is retarded 

 if their position is reversed w^ith respect to gravity (Megusar '07). 

 The sea-urchin egg develops more slowly than is normal after 

 being centrifuged; this is probably due to the resistance to cleavage 

 offered by the cap and pigment (Lyon '07, p. 166). McClendon 

 ('08) found the rate of division of centrifuged Paramecia to be 

 greater than that of normal animals. When seeds are centrifuged 

 and restitution is slow the growth is retarded (Andrews '03). 



Centrifugal force seems to have no influence upon the rate of 

 development of those beetles' eggs that produced normal embryos 

 and larvae. A large number of observations give the average 

 period for the development of the eggs of C. multipunctata, C. 

 bigysbyana and C. lunata as five and two-thirds days (Hegner '08, 

 a). In a great many cases normal eggs do not hatch under six and 

 one-half days. Practically all of the centrifuged beetles' eggs 

 hatched in six days. 



5 Eggs Centrifuged Before Deposition 



In the majority of cases the eggs laid by centrifuged beetles show 

 no rearrangement of material and the production of an embryo 

 or larva is not impeded. The exceptions to this are the eggs 

 described as Series C.B. 12; here two abnormal embryos were 

 produced by eggs which had been centrifuged within the mother 

 before the germinal vesicles had broken down. No definite cause 

 can be given for this irregularity. 



X SUMMARY 



I Eggs of Chrysomelid beetles when oriented in a centrifugal 

 machine with either their posterior or anteiior ends toward the 

 axis of rotation, and subjected to 1500-2000 revolutions per minute 

 for from one to twelve hours, become stratified into three lasers: 

 (i) a light vesicular zone at the inner end, (2) a heavy granular 



