I06 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



phragm {ph), has given birth to an ax-shaped process x for which 

 there is no equivalent among the insects. A branchial shaft {gl) is 

 attached externally to the base of the process. 



The region of the lateral wall posterior to the pleural apodeme is 

 very large.^^ It bears externally two branchial shafts {gl) ; in- 

 ternally, in the back part of the segment, we find a strong infolding 

 of the cuticle in the shape of a large triangular blade with a small 

 terminal spatula. We call this large blade the postpleural process 

 {ps). Does it proceed from the wall of the precoxopodite or does 

 it pertain to the primitive lateral body wall, which locally is not pressed 

 back ? We cannot answer this question at the present time. 



Near the proximal angle (y) of the coxal margin a f ureal apophysis 

 {fu) arises. It takes its rise at the edge of the sternal plate, at the 

 limit between this sternal plate and the membranous strip, the only 

 remnant, proximally, of the precoxal wall. This spot corresponds 

 to the spot which was pointed out by Weber (1928, p. 250) as typical 

 of every f ureal apophysis of the Pterygota.^" 



We have figured and described the postpleural process and the 

 furcal apophysis of Penaeus as separated from each other, as they will 

 be found after a specimen is treated with caustic potash. Without 

 this treatment, these two internal formations of the cuticle would have 

 appeared wrapped in a common subhypodermal sheath ^° pertain- 

 ing to an endoskeletal scaffolding (fig. 4) which we shall analyze 

 further on. In Camharus, an American crayfish, Snodgrass (1952, 

 p. 156) saw likewise a "pleural apodeme" united with a "sternal 

 apodeme" by certain "interlocking fimbriations" ; these parts become 

 disconnected, he explains, if the preparation is left to dry. 



We know that the schemes of the thorax depicted in general treatises 



1^ In going over the series of precoxopodites of Penaeus, we come across 

 some of them in which the two regions of the lateral wall are less unequal. 



^9 In a note written to do justice to all that may be valuable in Ferris's 

 ideas, one of us (Carpentier, 1947, pp. 300-301) has maintained that in the 

 insects, this one can pertain more to the proximal zone of the catapleural ring 

 than to the sternum itself. Rendering an account of this note, Weber (1952, 

 p. no) unfortunately wrote that the basisternite is regarded in that note as a 

 secondary formation. This is not correct. 



-•^ Let us keep in mind that we give this name to every endoskeletal scaffolding 

 directly prolonging inward the basement membrane of the hypoderm. Muscles 

 inserted on such an endoskeleton may be, of course, homologous with muscles 

 inserted on cuticular infoldings encompassed with the hypoderm and thus 

 with the basement membrane of the hypoderm (see Carpentier, 1946, pp. 171- 

 172), whatever the chemical nature — not yet elucidated — of the subhypodermal 

 formations. 



