88 BULLETIX: MUSEUM OF COMPARATIVE ZOOLOGY. 



My comparisons have been hindered by the scanty and fragmentaiy 

 nature of piibhshed enibryological observations upon the mouth-parts of 

 Arthropods. Detailed studies npon the subject in the less specialized 

 Pterygota, Crustacea, Ai*achuida, Diplopoda, and Chilopoda do not exist, 

 but are necessary for the proper understanding of the morpliology of the 

 mouth-parts, and will have much bearing upon the phylogeny of the 

 classes named. 



The present study was made under the supervision of Dr. C. B. Daven- 

 port, to whom I am most grateful for his constant, critical supervision, 

 valuable advice and encouragement. 



Professor E. L. Mark has carefully revised the text and attended to 

 all the details of publication ; his help, as always, has been of inestimable 

 value to me. 



Methods. 



For killing eggs, and adults as well, simply hot water was used, with 

 excellent results. After killing, material was carried through several 

 successively stronger grades of alcohol and finally preserved in absolute 

 alcohol. 



In the study of the embryo, both dissections and serial sections wei*e 

 made. As much as possible was learned by dissection, as that method, 

 although difficult, gave more trustworthy results than could possibly be 

 obtained by reconstruction from sections. The germ bands of freshly 

 killed embrj'os were too delicate to be dissected out uninjured ; but after 

 being in absolute alcohol for two months they had become sufficiently 

 hardened for this operation. A longer stay made them brittle, but 

 advantageously so in some respects. 



Dissections were made under a compound microscope with a magnifi- 

 cation of about one hundred and fifty diameters. For the finest work, 

 the "minutien Xadeln," used by entomologists for pinning minute in- 

 sects, were employed. The general form and position of an embryo 

 could be seen through the transparent egg-membranes ; but to get 

 clearer views, the outer membrane was removed, the remaining corru- 

 gated membrane punctured, and a staining fluid allowed to penetrate 

 the germ band. Preparatory to the dissection of minute structures, tlio 

 egg was placed in weak glycerine, which caused the embryo to shrink 

 away from the membranes slightly, allowing these to be removed ; tlie 

 germ band was dissected out and stained with Grenadier's alcoholic 

 boj"ax-carniine or hfciiiatoxylin. Isolated ])arts of the embryo were 

 mounted temporarily in weak glycerine without pressure, in such a 



