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WHEELER. [Vol. V 1 1 1 . 



open at the broad pole and gently pushing against the narrow 

 pole of the yolk with one needle, while holding on with 

 the other to the chorion at the same pole. In the earliest 

 and latest stages the chitinous blastodermic membrane comes 

 off with the chorion, in other stages it adheres firmly 

 to the yolk and prevents satisfactory staining. If aqueous 

 stains like Orth's lithium carmine or Grenacher's alum car- 

 mine are used, the eggs should be left in them but a short 

 time and carefully watched as the yolk-bodies have a peculiar 

 tendency to absorb water till they lose the polygonal shapes 

 they acquired by mutual pressure, finally swell and fall 

 asunder. This is especially liable to occur in the younger 

 stages when the blastodermic membrane is removed. I have 

 as yet found no other insect &gg with yolk capable of imbibing 

 so much water. In Grenacher's borax carmine there is no 

 swelling, a reason which has induced me to use this stain in 

 preference to the aqueous solutions ; though the two stains 

 mentioned give excellent results if used with due precautions. 

 After dehydrating and clearing with cedar oil, the eggs are 

 kept from two to three hours in melted paraffine (55° C). 

 Older embryos in which most of the yolk has been metabolized 

 need not remain in paraffine more than an hour. 



Embryos isolated from the yolk in the anatreptic stages, as 

 well as later embryos used in sectioning, were stained in Czo- 

 kor's alum cochineal. The bluish color of this stain is prefer- 

 able to the borax carmine in serial sections, as it is less 

 wearisome to the eye. 



In the study of the entire embryo three different methods 

 may be followed with advantage. 



Method I. — The isolated embryo is stained with borax car- 

 mine, all excess of the stain is removed by prolonged immersion 

 in acid alcohol, and the preparation mounted in clove oil or 

 balsam. In such preparations many of the details of internal 

 structure, such as the arrangement of the coelomic sacs, may 

 be very clearly distinguished. This method was very exten- 

 sively used by Graber; in fact it seems to have been the only 

 method which he employed for surface study. In this respect 

 it is decidedly inferior to 



