6 Hewitt, Note on the Buccal Pits of Peripatus. 



tures, such as tracheal pits and trachea in connection 

 with them, highly improbable. 



The muscles which work the jaw-levers are attached 

 to the dorso-lateral walls of the epithelial pocket, as 

 shown in the figures, chiefly about the anterior and 

 median portions of the rod, the larger muscles dis- 

 appearing towards the posterior extremity. They 

 consist of two series, a median series {^Fig. 2, liii) running 

 in a longitudinal direction enclosed by two transverse 

 bands of muscle {ini) which are attached to the greater 

 part of the dorso-lateral side of the epithelial pocket, 

 that is, to the whole surface of this side except in the 

 middle line (as shown in Fig. 2) and extend thence 

 dorso-Iaterally. The jaw-levers and their muscles dis- 

 appear opposite the beginning of the second pair of legs. 



Prof. Dendy has pointed out to me that Purcell (5) 

 has shown that in the Attidae, a group of spiders, " by 

 far the greater part of the tracheal system is nothing 

 else but a pair of modified ectodermal tendons." If 

 ectodermal tendons can be modified in this way,* the 

 question naturally arises, can these hollow chitinous jaw- 

 levers of Peripatus be compared with ectodermal tendons 

 which in the Attidae have become modified, according to 

 Purcell, to form tracheal structures. I do not think that the 

 hollow chitinous jaw-levers of Peripatus can be regarded as 

 structures of a respiratory nature. They are simply 

 skeletal structures, flattened for the better attachment of 

 the muscles which control them, and hollow like many 

 structures of a similar nature found in other Arthropods. 



* Korschelt & Heider (6) are inclined to trace back the origin of the 

 tracheae of the Arachnida to kings. Simmons (7) has found that the trachea 

 develop from foldings in the posterior surface of the third abdominal 

 appendage, which in their early stages are similar to those on the second 

 appendage, which give rise to the lung-books. He considers that tht; 

 trachea: are developed from a lung-book condition. 



