140 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
clusion that the tentorium of Anurida is derived from proliferated ecto- 
dermal cells which are in no way, except in position, distinguishable 
from young ganglion cells. 
In Anurida, as in Orthoptera (Wheeler, ’93, Heymons, ’95°) and 
Lepisma (Heymons, 97°), the ventral cords consist of dorso-ventral 
rows of cells, which arise by proliferation from the outer ectoderm, 
Although it has seldom been supposed that these cells became other 
than ganglionic in function, it may be assumed, in view of their origin, 
that ail of them are potentially chitin-forming cells, and it seems prob- 
able that some of them actually do form the chitinous tentorium. 
An oblique section of Stage 8, cut at a fortunate angle for studying 
the relation of tentorium to cells, gave the appearance represented in 
Figure 35. Contiguous to practically all parts of the tentorium, in this 
section, are cells the nuclei of which do not differ in appearance from 
nuclei of undoubted ganglion cells. On all sides of the tentorium such 
cells abound and closely embrace it ; an especially large mass of these 
cells occurs immediately under the frontal plate, in which, moreover, 
several cells always become enclosed and appear to be functional in the 
adult. I found no evidence which could be interpreted as indicating 
any other way of formation. 
Von Stummer-Traunfels (91) appears to have overlooked the ten- 
torium of Apterygota, for he mentions the “Stiitzapparate” only, by 
which he evidently means the structures I call ‘lingual stalks.” 
As regards the Thysanura, Meinert (’65, Tab. XIV. Figur 5, 6) men- 
tions in Japyx and Campodea a median chitinous plate, from which the 
mandibular adductors take their origin,.which is undoubtedly the tento- 
rium. Grassi (86°) also alludes to it in Japyx. 
In Machilis the lingual stalks, important in Collembola, become rudi- 
mentary ; and most of the mandibular and maxillary muscles become 
attached to the tentorium ; but they are fewer than in Collembola. The 
tentorium is thus described by Oudemans (’88, p. 186): ‘ Die vor- 
deren [Stiitzplatten] kommen von den Seiten des Clypeus, gleich ober- 
halb der Mahlhohle, wie dieses im Durchschnitt abgebildet ist in Figur 
32. Links und rechts geht dort die Chitinhaut des Clypeus tiber in eine 
Platte. Die beiden Platten niihern sich nach hinten, indem sie fortwih- 
rend breiter werden. In der Mitte des Kopfes kommen sie zusammen, 
sind da jedoch nicht verschmolzen, sondern nur stark durch Bindegewebe 
verbunden, Figur 19 Lt. Hinter dieser Verbindungsstelle weichen die 
Platten wieder auseinander, werden schmiiler und gehen, links und 
rechts vom (Hsophagus, nach oben. Zuletzt geht jede tiber in einen 
