CX1X 
the high development reached by the antenna, as well as the legs of 
Corethra, during the larva state, there seems no great improbability 
in this view. 
From a pupa of this kind to a pro-imago, as it has been called, of 
| Ephemera or Chloeon, there is but a step, even if so much. 
Tn fact the so-called pupa of Corethra ought to be called a pro- 
imago rather than a pupa. _Its functions, with one single exception, 
are in full activity. Though it does not feed, it swims and appears as 
active and vivacious as the larva. It can see perfectly well, and 
on the approach of danger darts rapidly to a place of greater 
security. 
Thus, then, it affords a remarkable illustration of the arguments I 
have elsewhere brought forward with the view of proving that the 
so-called larvee and pup are not homologous terms in different 
insects. Even among the Diptera, while in Corethra the wings 
_ and legs of the imago are already formed, and the mouth parts only 
require a slight final modification when the so-called larva turns 
into a pupa, at the corresponding period in Musca the very reverse 
is the case, and the head itself can scarcely be said to have any 
existence. 
Dr. Weissmann concludes his valuable memoir by a comparison of | 
the development of Corethra with that of Musca. 
In Corethra the larval segments develop themselves directly into 
those of the imago, and the appendages of the head into the corre- 
sponding organs of the perfect insect. The thoracic appendages are 
formed during the last stage of the larva, by outgrowths of the hypo- 
dermis round a nerve or a trachea, from the cellular envelope of which 
the cellular tissues in the interior of the organ are formed. The larval 
muscles in the abdomen are received almost unaltered into the imago. 
The muscles peculiar to the imago develop themselves, in the last 
larval state, from indifferent cellular bands, which are present even in 
the egg. The genital glands date from the embryo, and develop 
gradually ; all the other systems of organs pass directly, with little or 
no change, into the imago. ‘The fatty tissue is small. The pupa con- 
dition is short and active. 
In Musca the thorax and head rise independently from the corre- 
sponding parts of the hypodermis of the larva, and the abdomen only 
|through direct alteration of the eight last abdominal segments. The 
thorax and head develop themselves from “imaginal disks” which 
have their origin in the embryo, First, after the formation of the 
