242 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
called the Pupipara, which are closely related to the muscids. 
Leuckart (’57) early showed the striking similarity of structure of 
the larval and pupal forms of the Pupipara to those of the muscids; 
in a former paper (’93) I have emphasized the same fact; Miiggen- 
burg (’92) has homologized the mouth parts of all the pupipars with 
the fly’s proboscis; Brauer (’85) has shown that the Pupipara are 
degenerate flies and has placed them next to the Muscidae in his 
classification of the Diptera. 
The Muscidae are classical objects for the study of imaginal 
discs. It was with them that Weismann inaugurated the study 
of these interesting bodies, and, since the appearance of his first 
paper in 1863, Ganin, Kowalevsky, Van Rees, and many others 
have published the results of investigations of them. All of these 
studies, however, have been on the development of the discs during 
the larval and pupal period of the insect’s life. The embryonic 
history of the discs, which includes their origin and the first stages 
of growth, has not been studied ; and no positive information exists 
concerning them except a short statement contained in a paper by 
Graber (’89), which will be spoken of later on, and the preliminary 
paper by myself, mentioned above. 
Historical. 
1. Imagined Discs in the larva and Pupa. — Swammerdam 
(1737-38) was the earliest investigator to observe that fundaments of 
the imaginal thoracic appendages in the higher insects, and even of 
the head in some cases, do not appear first in the pupa, but are present 
in the larva. He was thus the first observer of imaginal discs. He 
showed that in the larva of Culex, Apis, and Pieris the fundaments 
of all the legs and wings lie beneath the thoracic integument. From 
his time down to the present generation no additions were 
made to the knowledge of the subject. Numerous investigators, 
however, made observations similar to those of Swammerdam. 
Lyonnet (1760) described and figured the two pairs of imaginal discs 
in the dorsal portion of the meso- and metatlioracic segments of the 
caterpillar, and added the supposition that they were the funda¬ 
ments of wings. Herold (T5) described the same discs, and cor¬ 
rectly interpreted them. Burmeister ( 35) also very accurately 
described the imaginal wing-discs of the caterpillar, as did Louis 
