500 
ZOOLOGICAL LITERATURE. 
Weismann, August. Die Metamorphose der Corethra plumi- 
cornis. Zeitschrift fiir wissensch. Zoologie, Band xvi. 
pp. 45-127, Taf. 3, 4 : 1866. 
In this most important memoir Weismann traces the deve- 
lopment of Corethra plumicornis through the various preparatory 
stages of its existence, indicating in great detail the mode of 
evolution of the various organs, and the manner in which the 
vital functions are performed at each step in the process of de- 
velopment. His concluding remarks are as follows ; — The 
pupa of Corethra evidently differs both morphologically and 
physiologically from the pupa of the Muscidre] it does not 
merely become the body of the imago, but is nothing else from 
the first, and requires only a slight perfecting to enable it to 
emerge as an insect capable of flight and reproduction. A 
pupa-sleep, in the literal sense, consequently is here entirely 
wanting \ all the functions of animal life go on uninterruptedly 
in the pupa, except that the inception of fresh nourishment 
ceases. All the processes which occupy the period of latent 
vitality in Musca, during which the blood no longer circulates, 
and every sensation and movement, as well as inception of food, 
ceases — all the processes which may be comprised under the 
term ^formation of the pupa^ take place in Corethra within 
the larval period, and the pupal period here can be compared 
only to the last two days of the Muscide pupa, in which the 
imago is already near perfection, so that when artificially freed 
from the cask-like shell it is already more or less capable of 
moving and living. 
From all this we may distinguish two diametrically opposite 
forms of insect-metamorphosis : — one represented by Corethra^ 
approaching most nearly to development witliout metamorphosis ; 
the other by Musca, departing most widely from the ameta- 
bolous development, and representing the most extreme form of 
metamorphosis In the one case a continuous, in the other 
a discontinuous development takes place ; and the two 
forms maybe briefly characterized as follows ; — 
Type Corethra : — The segments of the larva are converted di- 
rectly into the corresponding segments of the body of the imago, 
the appendages of the head into the corresponding ones of the 
head of the imago ; those of the thorax are produced after the 
last moult of the larva as diverticula of the hypodermis round 
a nerve or trachea, from the cellular envelope of which the for- 
mation of tissue in the interior of the appendage issues. The 
larval muscles of the abdominal segments are transferred un- 
changed into the imago ; the thoracic muscles peculiar to the 
imago, as also some additional abdominal muscles, are developed 
in the last larval periods from indifferent cellular cords which are 
indicated even in the egg. The genital glands date back to the 
embryo, and are gradually developed ; all the other systems of 
