248 MYRIOPODA. 



of the antennae contains a large diverticulum of a segmental cavity 

 (Fig. 127, h.us and at). The conclusions on this point in connection 

 with Peripatus (p. 186) would therefore also apply to the Myriopoda. 

 In any case the diverticula of the segmental cavities that extend into 

 the limbs seem to be a primitive condition which is lost later, and, 

 among the Insecta, is only retained in the lower forms (e.g., Orthop- 

 tera, Graber, Cholodkowsky, Heymons, etc.). 



The Body-cavity, the Blood-vascular System, the 

 Fat-body, and the Musculature. 

 The stage in which the mesoderm is represented by two rows of 

 consecutive primitive segments does not last long. According to 

 Heathcote each primitive segment divides into two vesicles, one of 

 which remains in the body (somatic part of the coelom), while the 

 other lies in the limb (pedal or crural part of the coelom), a condition 

 which may be compared with the similar distribution of the primitive 

 segments in Peripatus. 



There are certain differences in detail in the further development of these 

 two parts of the primitive segments in Peripatus and in the Myriopoda, but 

 this subject, in spite of Heathcote's observations, is still somewhat obscure, 

 and a more detailed study of it is very desirable. 



In tracing the development of the primitive segments from before 

 backward, we find that the first segment, the pedal section of which 

 lies in the antennae, is used chiefly for the formation of the antennal 

 musculature and for the musculature of the head generally. The 

 primitive segments of the mandibles are in the same way concerned 

 in the formation of musculature, but those of the maxillary segment 

 have, according to Heathcote, another significance (formation of 

 the salivary glands), which will be discussed below. 



From the first trunk-segment onward, the two sections of the 

 coelom show throughout a difference in their ultimate development. 

 While the pedal coelomic sacs are used for the development of the 

 leg-musculature and lose their sac-like form, the somatic parts, in 

 the Diplopoda, shift towards the middle line and come to lie above 

 the ventral chain of ganglia and here later fuse with one another. 

 They thus differ from the corresponding parts in Peripatus, which 

 shift dorsally and come into contact above the intestine (p. 208 and 

 Fig. 102, p. 205). Here, however, as there, they form the genital 

 glands, and since, in the Chilopoda, these lie dorsally to the intes- 

 tine, we might expect in these forms greater agreement with the 

 arrangement in Peripatus than is found in the Diplopoda. 



