116 
Wisconsin Academy of Sciences , Arts and Letters. 
C. The Gland Hypothesis. 
Besides Patten, who claimed that the pleuropodia might be glands [’84] 
no one till very recently has considered this view. In the July number of 
the American Naturalist [’89a] I advocated this view in a brief note.* In 
one of the August numbers of the “ Biologisches Centralblatt ” [’89] Graber 
published his remarks on the pleuropodia of Stenobothrus, attributing to 
these organs a glandular function. In one of the September numbers of 
the “ Zoologischer Anzeiger” [’89b] a preliminary account of my observa¬ 
tions on the pleuropodia of Zaitha and Cicada was published. In one of 
the October numbers of the “ Biologisches Centralblatt” appeared J. Nus- 
baum?s description of the pleuropodia of Meloe [’89]. Nusbaum regards 
these organs as glandular, but terminates his paper in a confusion of 
ideas as evinced by the following remark: “ Die druesige Natur der 
Bauchanhgenge bei den genannten Insekten [Meloe, Stenobothrus ] [die oline 
Zweifel aucli bei anderen gefunden werden wird] spriclit dafuer, dass wil¬ 
es hier walirscheinlich mit rudimentaeren Organen, die nicht bloss zur 
gewoehnliclien Gangfunktion bei den Insektenvorfahren, sondern vielleicht 
auch noch zur Atmungsfunktion dienten, zu thun haben.” 
I fail to comprehend how the glandular nature of the pleuropodia can in 
any way suggest that they may have functioned simultaneously as ambu¬ 
latory and respiratory organs. 
The following are my reasons for assigning a glandular function to the 
pleuropodia: 
1. The entire ectoderm of Arthropods, excepting its nervous derivatives, 
is essentially a glandular layer, one of its prime functions being the secre¬ 
tion of the chitinous armour so characteristic of these animals. This 
function is retained by the ectoderm cells, even when they are pushed into 
the body as in the case of the tracheae, tentorium, oesophagus and rectum. 
Looking at the compound Arthropod eye from Watase's standpoint [’89] 
as a cluster of ectodermic invaginations we have a case where ectodermic 
cells still retain their chitin-secreting habits though pushed below the sur¬ 
face of the general integument and covered by superjacent cells. 
2. The pleuropodial cells closely resemble other simple ductless glands 
in insects, such as the wax-glands of the Aphididae and the stinging 
glands of some Lepidopterous larvae. In the embryo and young larvae of 
the Bombycid Hyperchiria io, I have observed the formation of the huge 
branching spines, which arranged in several parallel rows, repel the insects 
enemies with their stinging secretion. The immensely enlarged ectoderm 
cells which secrete the poison in the lacunae of the spines, have very 
glandular cytoplasm and large nuclei, thus resembling the pleuropodial cells 
of Blatta. 
3. The pleuropodial cells in several insect embryos produce a secretion, 
the character of which differs considerably in different forms. 
* This number of the Naturalist did not appear till Nov. 18th, 1889. 
