558 WILLIAM PATTEN. 



Occasionally it is necessary to partly unroll the sections. 

 In this case care should be taken not to use too much clove oil 

 in softening the shellac^ or the sections will not adhere firmly 

 enough to allow them to be unrolled. The shellac is also more 

 adhesive if put on the slide just before using. With attention 

 to these details, a roll of paraffine will adhere firmly to the 

 slide, and then may be easily unrolled by means of a fine- 

 pointed needle. When all the sections have thus been placed 

 in rows upon the slide, it is warmed, melting the paraffine, and 

 allowing the sections to lie smoothly on the surface. A very 

 important point is not to warm the slide too quickly, for if 

 there are any sections which do not lie directly on the surface, 

 the paraffine which holds them together will melt and let them 

 fall to pieces before they have had a chance to fasten themselves 

 to the shellac. Hence the slide should be warmed very 

 gradually, and the sections made so flexible that they fall of 

 their own weight into place without the paraffine being actually 

 melted. Moreover, if the slides are heated too much, the 

 shellac and paraffine will unite to form a whitish film, which 

 often destroys the value of the preparation. After cooling the 

 paraffine is dissolved in turpentine or benzole, and the sections 

 mounted in Canada balsam. By this method one hundred 

 sections have been cut from an egg which was one 

 hundredth of an inch in diameter, or, in other words, a nearly 

 complete series of sections each of which was only a little more 

 than one four hundredth of a millimeter thick. 



III. Historical. 



In spite of the innumerable works which have been published 

 concerning the anatomy and habits of insects in general, very 

 little notice has been taken of their embryology. It is remark- 

 able that while our present insufficient knowledge has pointed 

 out such a diversity in the development of closely related forms, 

 that so little attention should have been given to the develop- 

 ment of the different groups. The Phryganids, however, have 

 received their proportionate share of attention, since already 

 we have six more or less fragmentary observations concerning 



