Centrifugal Force upon Beetles' Eggs 509 



are laid. In the case of Calligrapha multipunctata and C. bigs- 

 byana the eggs can be definitely oriented as is explained in the 

 next part of this paper. A number of beetles were kept in the 

 laboratory and the eggs were marked on the anterior-ventral sur- 

 face with a small spot of waterproof india ink. The exact time of 

 deposition was recorded in all cases. The eggs are not always in 

 the same stage of development at the time of laying, but all those 

 in one batch are approximately in the same condition. When the 

 eggs had developed to the desired point they were placed in small 

 indentations in a block of paraffin. The entire block containing 

 the eggs was then lowered to the bottom of a glass tube of an 

 ordinary water-power centrifugal machine. The eggs were then 

 15 cm. from the axis of rotation. The number of revolutions per 

 minute was not accurately determined, but was probably between 

 1500 and 2000, although in some cases (those described in experi- 

 ments C. M. I and L. D. i and 2) a slower rate of speed was used 

 (360 revolutions per minute). The eggs when taken from the 

 centrifugal machine were left in the cavities in the paraffin block 

 with the heavy end down until they were fixed. In previous work 

 I found a modification of Petrunkewitsch's fluid the best for killing 

 and fixing the eggs. This was used entirely for the centrifuged 

 material, although control eggs were fixed in a number of the 

 common mixtures. Kggs were stained in toto with Mayer's 

 haemalum acidulated with 2 per cent of glacial acetic acid, or with 

 alum cochineal. Sections were stained on the slide principally 

 with haemalum followed by Bordeaux red. 



One difficulty in doii.g experimental work with the eggs of Calli- 

 grapha is that only a few are laid at one time (eight is the average 

 number) and, as the coi ditions of the experiments frequently are 

 resporisible for the destruction of some of these, no series contains 

 very many successive stages. 



There are also causes for trouble in making preparations. In 

 some it stances the eggs stuck fast to the chorion at the outer end, 

 where the contents had been strongly driven against it; the chorion 

 could not be removed from these without injury to that part of the 

 egg. After eggs have been centrifuged they are more difficult to 

 section than before because the large deutoplasmic spheres collect 



