140 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



elusion 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 

 Le'pisma (Heymons, 97^), the ventral cords consist of dorso-veutral 

 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 all 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 tiie 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 he functional in the 

 adult. I found no evidence which could be intei-pi'cted as indicating 

 any other way of formation. 



Von Stumraer-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, b) 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 ai'e fewer than in Collembola. The 

 tentoriiim is thus described by Oudemans ('88, p. 18G) : " Die vor- 

 deren [Stutzplatten] kommen von den Seiten des Clypeus, gleich obor- 

 halb der Mahlholile, wie dieses im Durchschnitt abgebildet ist in Figur 

 32. Links und rechts geht dort die Chitinhaut des Clypeus iibcr in eino 

 Platte. Die beiden Flatten nS,hern sich nach hinten, indem sie fortwah- 

 rend breitcr werden. In der Mitte des Kopfes kommon sie znsamnicn, 

 siud da jedoch nicht verschmolzen, sondern nur stark durch Bindogewebe 

 verbunden, Figur 19 L^. Hinter dieser Verbindungsstelle weichen die 

 Flatten wiedcr auseinander, werden schmiiler und gehon, links und 

 rechts vom (Esophagus, nach obon. Zuletzt geht jcdo iiber in eiuoa 



