THE HEART AXD THE SALIVARY GLANDS. 251 



the cavities of the pseudocoele. Ventrally to the heart a peri- 

 cardial septum forms, which has the same origin as the heart itself 

 (Heathcote). 



According to Sograff, the heart of Geophilus arises from a series 

 of paired cell-accumulations lying on the already formed intestine 

 (Fig. 128 A). When it is said that these belong to the splanchnic 

 layer, the splanchnic layer proper of the primitive segment can 

 hardly he intended, but rather one of the coverings of the intestine 

 derived from the parenchymatous tissue. This is the sense in which 

 Heathcote also speaks of a splanchnic and a somatic layer (Fig. 

 126, sp and so). In the cell-accumulations, each pair of which 

 corresponds to one of the chambers of the adult heart and to a 

 body-segment, cavities appear (Fig. 128 B). The two sacs belonging 

 to each pair fuse together, uniting in the middle line, and thus form 

 a chamber of the heart, and the consecutive chambers, uniting 

 together, form the whole dorsal vessel (Fig. 124). The heart in 

 its development closely resembles the dorsal vessel of the Annelida 

 which is derived from paired rudiments (Vol. i., p. 291), and, if 

 this account of its origin prove correct, the Chilopoda would appear 

 to show in this respect a still more primitive condition than is found 

 even in Peripatus. 



The body-musculature arises out of the mesodermal elements which 

 become applied to the ectodermal body-wall, but, as we said before, 

 nothing certain is known of the derivation of these elements. 



e> 



The Salivary Glands. 



Although one cannot but be predisposed to homologise the salivary 

 glands of the Myriopoda with those of the Insecta, and therefore to 

 regard them as ectodermal structures, we are compelled by Heath- 

 cote's statements to consider them as mesodermal. The salivary 

 glands are said by him to be formed as tubular outgrowths of the 

 somatic portion of the primitive somite of the maxillary segment, 

 i.e., the inner division of the primitive segment (p. 248). When the 

 tube has grown to some length it opens externally by fusing with the 

 ectoderm on each side at the base of the maxillary plate. 



Should the origin of the salivary glands out of the mesoderm actually be con- 

 firmed, we should have to regard them as transformed nephridia, whereas the 

 salivary glands of the Insecta, in consequence of their ectodermal origin, must 

 no doubt be considered as crural glands. The salivary glands of the Myriopoda 

 would then be formed in the same way as those of Perijxdits (p. 206), although 

 in the latter it is the lateral not the inner portion of the primitive segment that 

 gives rise to them. The question as to the direct homology of the salivary 



