INSECTA. 
151 
must become absorbed ; in the same way, for example, in the legs, the 
muscles, &c., belonging to them must shrink up. Besides legs, the bran- 
chiae of the larvae of ditferent insects — their simple eyes (which the author 
very correctly does not consider as corresponding to the future compli- 
cated eyes of the complete insect), — also the salivary vessels, and the 
jaw-feet of many Decapoda, which are afterwards absorbed, belong to 
the organs which are lost by the retrograde metamorphosis. This meta- 
morphosis shows itself in the most striking manner, where the animals 
are fixed in the last stages of life, as the parasitic Crustacea and the 
Lepades. The consequences which the author draws from his researches 
are, — 1st, That when, through the retrograde metamorphosis, a part has 
shrunk up, or even completely disappeared, another has normally formed 
itself, which compensates for it, or undertakes its function : 2d, That in 
rarer cases, a part of the body only, at one place, undergoes an absorp- 
tion, whilst another is more highly developed ; and, 3d, That by way of 
exception, individual portions of the body are lost without being replaced 
by others, as is chiefly the case in the lower Crustacea, where the author 
supposes, that all the functions, and with them also their organs, yield 
to the very highly important development and activity of the organs of 
propagation. 
Kolliker has carefully investigated the incipient develop- 
ment of particular insects, viz., — the formation of the larva 
in the egg of the Chironomus zonatus, which forms the Alga 
gloconema ; of the Simulia canescens, Bremi, and of Donacia 
crassipes (?). (Observationes de prima Insectorum genesi ad- 
jecta articulatorum evolutionis cum vertebratorum conipara- 
tione, Diss. Inaug. Scr. Alb. Kolliker. Turic. 1842, 3 tab.) 
In the comparison with the development of the vertebrata, the author 
has arrived at the following conclusions : — 1. In articulated animals, the 
germinating tissue is divided into a serous and mucous fold : 2. From the 
primitive part of the serous fold, the abdominal plates (visceral platten) 
sprout out towards the yolk, grow over it, and unite upon the yolk side 
of the egg; upon the opposite side of the fold are formed the dorsal 
plates ; they do not grow together, but form themselves into the hind 
limbs : 3. The wings of insects are the lateral limbs : 4. The first traces 
of the vertebral column show themselves in the chain of abdominal 
muscles situate between the nerves and the intestinal canal : 5. The 
nerves (animalischen nerven) take their origin in the outer part of the 
serous fold ; they are not, however, enclosed in a canal, but only covered 
by skin, as the dorsal plates are not united ; the ganglion of the brain 
also takes its origin from the primitive part : 6. The organs of sense 
195 
