96 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL.97 



mesoderm bands extends upward from the junction of the head-lobe 

 with the trunk and meet over the stomodaeum" (fig. 41 A, Msd). 

 The same is true of Caraushis (B), as shown by Wiesmann (1926), 

 but in the crustacean Heinimysis, according to Manton (1928), a 

 part of the preoral mesoderm has an independent origin from the 

 germ band. 



Among the Chelicerata the cephahc mesoderm is less developed 

 or differentiated than in the Mandibulata. In Limulus longispina, as 

 described by Kishinouye (1893), the first pair of coelomic sacs in 

 the embryo occupies both the cephalic lobe and the cheliceral somite. 

 Later these sacs become partially divided by an incomplete septum 

 into a pair of cephalic sacs and a pair of cheliceral sacs, but the latter 

 soon disappear. In the scorpion, according to Brauer (1895), the 

 cephalic coelom is an extension of the coelomic cavities of the chelic- 

 eral somite, and is never shut off from the latter in a pair of specific 

 head sacs. Likewise in the Pedipalpida {Thclyphomis) Schimkewitsch 

 (1906) says the coelomic sacs of the head segment are continuous 

 with those of the cheliceral segment. Kishinouye (1894) finds, on 

 the other hand, in the Araneida (Lycosa and Agclena) a pair of 

 coelomic sacs in the cephalic lobe that are entirely separate from the 

 sacs of the cheliceral somite. The cephalic sacs are later divided each 

 into two parts ; the ventral sections disappear, the dorsal sections 

 elongate upward and form between them the cephalic aorta. 



In the Mandibulata coelomic cavities associated with the first 

 antennae are of common occurrence in the cephalic mesoderm. A 

 diverticulum from each antennal sac extends into the corresponding 

 antenna (fig. 41 C, AntCS) and gives rise to the antennal muscula- 

 ture. The inner dorsal parts of the sacs, as observed by the majority 

 of investigators (see Wiesmann, 1926, Roonwal, 1937), grow mesally 

 into the space between the stomodaeum and the brain, where they 

 extend anteriorly and posteriorly and form the cephalic part of the 

 aorta, including the anterior end of the tubular aorta proper, and an 

 open distributing section that extends from beneath the brain to the 

 clypeal region. The cephalic aorta of the crustacean Hemimysis, 

 however, is said by Manton (1928) to be a product of the preantennal 

 mesoderm. 



The presence of preantennal coelomic sacs associated with small 

 evanescent rudiments of preantennal appendages (figs. 42 A, 43 A, 

 Prnt) is recorded by Heymons (1901) in Scolopcndra (fig. 42 B, 

 PrntCS), and by Wiesmann (1926) in Carausius (F, PrntCS), and 

 the occurrence of coelomic cavities in the preantennal mesoderm of 

 Hemimysis is reported by Manton (1928), though vestiges of pre- 



