and the Genealogy of the Arthropoda. 453 
which is destitute of appendages, is composed of ten segments. 
By the fusion of the head and three thoracic segments we get 
the primary form of the Arthrogastres (Scorpions, &c.), and 
by the further fusion of the abdominal segments into one piece 
the Spherogastres (true Spiders). 
_ The Myriopoda have broken out from some early insectan 
branch. This is clearly shown by their embryonal form. and 
development ; for the embryos possess only three pairs of legs, 
and perfectly resemble larve of insects. Moreover the in- 
Beil anatomy of the Myriopoda is so nearly related to that 
of insects that there can be no doubt of the fact of their 
derivation. The great number of body-segments, and con- 
sequently of legs, is a subsequent addition, acquired after the 
branching off, as is proved by their development, and is also 
shown by the analogy of many Crustacea (Kdriophthalma). 
Thus we come to the true Insecta. Here, following the 
example of Fritz Miiller and Hickel, we must in the first place 
dispose of a strong prejudice, namely, the principle of classifi- — 
cation according to the ‘complete’’ or “ incomplete” meta- 
morphosis. ‘This is now-a-days a perfectly untenable prin- 
ciple. We now know not only what is the significance of 
metamorphosis in general and what we are to conclude there- 
from, but we have also learnt, thanks to the brilliant investi- 
gations of Fritz Miller upon the Crustacea, what modalities 
may affect the metamorphosis, lengthening, abridging, or 
altering it; and we know that the so-called ‘ perfect’’ meta- 
morphosis of many, and perhaps of all insects, has been 
acquired during ontogenesis (and ‘not inherited from the ori- 
ginal progenitor). Moreover we have obtained from the facts 
the abstraction that the metamorphosis is always abridged in 
proportion as more generations follow one another, and that 
the tendency of the organisms (if we may use the expression) 
is always striving to attain, by the shortest possible way, from 
_ the egg state to the perfect, sexually mature animal. Tor this 
reason I have already indicated how important, and how rich 
in unexpected results, a comparative investigation of larvee 
will be. One of the most striking examples of a perfect dif- 
ference of metamorphosis, with the greatest similarity in its 
starting and finishing points (the egg and the sexually mature 
animal), is presented by a species of the genus Gecarcinus, a 
-Brachyurous Crustacean which, like the Crayfish, quits the 
egg at once in its definitive form, whilst all other crabs, and 
eyen all other species of the genus Gecarcinus, only attain 
their definitive form after passing through a metamorphosis. 
Similar peculiarities will certainly be presented to us by a 
careful investigation of larva, and the notions of complete and 
