No. 2.] BLATTA AND DORYPHORA. 343 
lopes and the dorsal organ formed soon after their rupture. 
For the sake of clearness I shall here consider only the envel- 
opes and relegate the discussion of the dorsal organ to my 
remarks on the revolution of B/atta and Doryphora at the end 
of the next descriptive division of my subject. 
Various theories, all more or less vague and intangible, have 
been advanced by different investigators to account for the 
amnion and serosa. Balfour (2) regarded these membranes as 
possibly derived from an early ecdysis. Ayers (1) refuted 
Balfour's suggestion; but as he started out in his own explana- 
tion with incorrect suppositions regarding the homologies of 
the different germ-layers in insects with those of other animals, 
he could not fail to involve the amnion and serosa in the gen- 
eral error. Kennel (24) regards the embryonic membranes of 
insects as homologous with the so-called ‘““amnion” in Perzpatus, 
and both structures as the remains of the trochosphere of the 
annelid ancestor. Emery (11) suggests that the envelopes may 
be homologous with the shell of the Entomostraca. 
The question as to the meaning of the envelopes in insects 
has been greatly confused by drawing in the widely different 
envelopes of Peripatus, Scorpions and Myriopods and the Crus- 
tacean dorsal organ, presenting all the different forms observed 
in Oniscus, Asellus, Cymothoa, Mysis, etc. Some authors agree 
with Kennel in regarding the embryonic envelopes throughout 
the Arthropoda as homologues. According to others the dorsal 
organs of the Crustacea are the homologues of the amnion and 
serosa of hexapods. Still others maintain that the Crustacean 
dorsal organ is to be brought into connection with the occasion- 
ally similar dorsal organ of insects. 
Will (52) has of late advanced a theory to account for the 
formation of the embryonic envelopes of insects only. His 
theory has the advantage over its precursors in that it replaces 
such indefinite terms as “early ecdysis,” “shell of the Entomo- 
straca,’ and “Trochosphere” by facts derived from the com- 
parative morphology of the membranes themselves. As I came 
to essentially the same conclusions as Will long before reading 
his article, I may be pardoned for presenting the subject in my 
own words, though they repeat in great measure what has 
appeared in Will’s paper. 
The problem as to the meaning of the amnion and serosa is 
restricted to the Hexapoda by postulating the following : — 
