588 



CLASS III. MYRIAPODA. 



The generative glands (Fig. 350) are unpaired elongated 

 tubes, the paired ducts of which open (p. 586) on the 2nd or 

 3rd body segments. They are placed on the ventral side of 

 the gut and develop, as in Peripatus, from the dorsal divisions 

 of the embryonic somites (Heathcote). 



All Diplopoda are, so far as is known, oviparous. The eggs 



are laid, shortly after copulation, in masses in damp earth, under 



stones, etc. Sometimes a kind of nest is made, and in some species 



the mother keeps watch over the eggs (Julus, Polydesmus etc.). 



Development.* The ovum is of fair size and contains a 



considerable quantity 

 of yolk. The nucleus 

 of the unsegmented 

 zygote lies in the centre 

 of the ovum in a little 

 protoplasm. It here 

 divides by a series of 

 binary divisions, each 

 product being s u r- 



rounded by a little 

 protoplasm. When a 

 certain number of 

 nuclei have been formed, 

 some of them with their 

 protoplasm migrate to 

 the surface and form 

 outside the ovum a 

 nucleated layer which 



FIG. 350. Generative organs of Glomeris marr/inata Constitutes the blasto- 



(after Fabre). T testes ; Of ovary ; Od oviduct. , , . . 



derm and gives rise to 



the ectoderm. The yolk usually becomes divided at about this 

 period into pyramids which give a superficial aspect of complete 

 cleavage, but it is not clear that each of these contains a nucleus. 

 The blastoderm acquires a keel-like thickening over part of its 

 extent. The mesoderm bands are derived from this. The nuclei 

 which remain in the yolk give rise to the endoderm, and possibly 

 some of them may apply themselves to the keel and participate 



* Korschelt and Heider, Textbook of Embryology of Invertebrates, English 

 Translation, vol. 3, 1899, Swan Sonnenschein & Co., where the literature 

 to date will be found. F. G. Heathcote, op. cit. E. Metschnikoff, Embry- 

 ologie der doppeltfiissigen Myriapoden, Z.f.w.Z., 24, 1874. 



