42 Wisconsin Academy of Sciences, Arts and Letters . 
oesophagus we find an epithelial layer, which is represented 
chiefly by ovoid nuclei, between which no cell boundaries are 
discernible. The multinucleated glands and their canals have 
here entirely disappeared. External to this epithelial layer 
lie the longitudinal muscles, and outside of these, the circular. 
The circular muscles at the anterior end of the oesophagus are 
from three to four layers in thickness, hut in the thoracic re¬ 
gion there are rarely more than two layers. In the thoracic 
region the circular muscles do not always encircle the oesopha¬ 
gus at right angles to its long axis, hut often run obliquely. 
The circular muscles are covered externally by a peritoneal 
membrane. 
Bordas (3) has extended his researches to several genera of 
Hymenoptera; he finds that families which are not closely re¬ 
lated—Bombinae, Sphecinae, Yespinae, Polistinae, etc.— 
show a great similarity in the structure of the alimentary 
canal. His results for all these being nearly the same, he 
takes as a type of his description Vespa crabo. Eor this 
species he describes (p. 272) the muscular layers of the oesoph¬ 
agus and crop as follows:—“Ils comprennent, en allant de 
Finterieur vers l’exterieur, une couche chitinense, incolore, 
generalement peu epaisse et reposant sur une tres mince couche 
cellulaire; vient ensuite une enveloppe musculaire formee par 
des fibres circulates, abond antes surtout a la base des sinuosites 
rentrantes; enfin, exterieurement existe une assise constitute 
par des faisceaux musculaires longitudinaux.” In a later 
work (5, p. 361), he again describes the muscular layers of 
Vespa crabo as follows:— 
“Man findet demnach auf einem zur Achse senkrechten 
Schnitte, von aussen nach innen gehend, die folgenden ver- 
schiedenen Schichten: 
1. Eine sehr feine peritoneale Membran, die sich fiber 
den Oesophagus, Kropf und ganzen Darm ausdehnt (mp). 
2. Eine erste Lage von Bingmuskelfibrillem, die durch die 
fast regelmassige Uberlagerung von zwei oder drei Schichten, 
welehe fiberall dieselbe Dicke besitzen, gebildet wird (fc). 
3. Langsmuskeln (ft). Diese letzeren sind in Bfindeln von 
verschiedener Zahl amceordnet. Die auf dem Querschnitt 
