GENERAL CONSIDERATIONS. 253 



of nephridia. A displacement of the genital aperture by the occurrence of 

 an additional segment behind this, the penultimate segment, and by the dis- 

 appearance of anterior segments seems altogether improbable. 



The position of the genital glands themselves appears to us more primitive 

 in the Chilopoda than in the Diplopoda, and like that of their efferent ducts, 

 more nearly to correspond to the condition in Peripatus. The glands lie 

 dorsally to the intestine, and in the embryo appear as two accumulations of 

 cells near the dorsal vessel (Fig. 128 B, cj). Their origin is, unfortunately, 

 as yet obscure. 



[An important contribution to the ontogeny of the Chilopoda has recently 

 been made by Hetmons (No. III.). This author has entirely reinvestigated the 

 development of Scolqpevdra, but unfortunately so far has only published a short 

 summary of his results. He finds that the egg possesses a central unsegmented 

 yolk containing segmentation-nuclei ; some of the latter migrate to the surface 

 and form the blastoderm, while others remain within the yolk and give rise to 

 some yolk-cells. The yolk-cells also arise as immigrants from all parts of the 

 blastoderm, as also do the entodenn-cells. There is no gastrula-groove. The 

 body is found to consist of the following segments : — a primary cephalic plate 

 and a primary anal piece (telson), between which are found (1) an antennular, 

 (2) an antenna], (3) an intercalary, (4) a mandibular, (5, 6) two maxillary, (7) a 

 maxillipedal, (8-28) the body-, and (29, 30) the genital segments. The salivary 

 glands are purely ectodermal and not modified nephridia. A coelomic cavity 

 is present in each segment, cephalic plate and telson excepted, in all thirty 

 pairs. The unpaired gonad and genital duct of the adult are paired in the 

 embryo, and arise in connection with the coelom ; as in the Insecta, the ducts 

 have ectodermal terminations with accessory glands. For the brain, see foot- 

 note, p. 241. Heymoxs concludes that the Chilopoda show close relationship 

 to the Hexapoda and are very remote from the Diplopoda, the Myriopoda not 

 forming a natural group. — Ed.] 



General Considerations. 



In considering the ontogeny of the Myriopoda, two important 

 questions arise — (1) whether the developmental history of the 

 Myriopoda testifies to their near relationship to Peripatus, and (2) 

 in what way their ontogeny is related to that of the Insects. Since 

 the Myriopoda appear in a certain sense as intermediate forms 

 between the Insecta and the Onychophora, these questions naturally 

 suggest themselves. It must at once be stated that up to the 

 present time the ontogeny of the Myriopoda is too little known 

 to enable us to answer these questions in a manner as satisfactory 

 as might be desired. 



Even with regard to the first ontogenetic processes in the Myrio- 

 podan egg, we must hesitate in instituting a comparison with 

 Peripatus. A superficial cleavage accompanied by segmentation of 

 the yolk takes place in the eggs of the Myriopoda, and the same 

 kind of cleavage has been affirmed of the egg of Peripatus novae- 

 zealandiae, which is rich in yolk (Fig. 76 A, p. 167). The eggs 

 of other species of Peripatus undergo total cleavage as has been 

 seen, but this method of cleavage was regarded as probably 



