88 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
My comparisons have been hindered by the scanty and fragmentary 
nature of published embryological observations upon the mouth-parts of 
Arthropods. Detailed studies upon the subject in the less specialized 
Pterygota, Crustacea, Arachnida, Diplopoda, and Chilopoda do not exist, 
but are necessary for the proper understanding of the morphology 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 were 
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 embryos 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 Nadeln,” 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, the 
egg was placed in weak glycerine, which caused the embryo to shrink 
away from the membranes slightly, allowing these to be removed ; the 
germ band was dissected out and stained with Grenacher’s alcoholic 
borax-carmine or hematoxylin. Isolated parts of the embryo were 
mounted temporarily in weak glycerine without pressure, in such a 
