and the Genealogy of the Arthropoda. 451 
genealogical tree of the Arthropoda, which must possess a 
special interest for the readers of this journal. 
Hiickel derives the Vermes and Arthropoda from a common 
root, which stood in genetic connexion with the Infusoria, 
and from which the Rotatoria have also originated. The Ar- 
thropoda then divide into two large sections (Cladus) :—the 
Carides, Crustacea (Branchiferous Arthropoda); and the Zra- 
cheata, Insects (Tracheiferous Arthropoda). Hiickel very 
correctly justifies this division by saying that the orders of 
Arachnida, Myriopoda, and Insecta are more closely connected 
than certain families of the Crustacea; and it seems pretty 
certain that the ‘'racheata were only developed from the 
Carides. Paleontology, indeed, furnishes but little evidence 
upon this point; but more is offered by the developmental 
history of individuals ; and it is well known that the larve of 
certain Neuroptera for a long time retain branchial respiration, 
which they only subsequently exchange for tracheal respira- 
tion. As, however, it is to be regarded as an established law 
that the development of an animal in the egg and in the 
larval state (the ontogenetic development) is only an abridged 
and partially obscured picture of the development of a genea- 
logical tree (the phyletic development), we are justified (as 
also for many other reasons) in drawing this far-reaching con- 
clusion as to descent from so remarkable a phenomenon as the 
change in the mode of respiration in the larvee of Neuroptera. 
Hence, also, developmental history, the study of which has 
now been taken up with fresh vigour, acquires an extraor- 
dinary importance ; and it is to be hoped that the necessary aid 
will not be denied on the part of entomologists: and this will 
consist essentially in their undertaking a description and sys- 
tematization of the larve as well as the description and clas- 
sification of the perfectly developed insects, and in ascertaining 
by observation the external changes which the body of the 
larva undergoes until it becomes transformed into the perfect 
insect. 
I will not enter into the details of the development and 
descent of the Crustacea, but only refer to the hypothetical 
order of the Zoépoda, which, according to the concordant opi- 
nions of Fritz Miiller and Hiackel, included the progenitors of 
the Schizopoda (Mysis, Huphausia), and consequently of the 
chstopoda, Decapoda, and all the Edriophthalma originating 
from these, as also of the Tracheata. The assumption of this 
order is founded upon the Zoéa, so well known to all crustaceo- 
logists, a developmental form in the ontogenesis of most 
Podophthalma, which refers us back to the Zoépoda. The 
unknown common original form of the Arachnida, Myrio- 
