250 



MYRIOrODA. 



gradually absorbed. It can still be traced in the cellular network 

 in the form of somewhat large structures resembling oil drops, which 

 represent the fat-body of the larva. With the gradual absorption 

 of the yolk and the simultaneous further development of the meso- 

 dermal elements, the primary body-cavity of the Diplopoda (Figs. 

 125 and 126 B), formerly filled with the compact mass of yolk, 

 passes at first into a pseudocoele formed of a cellular network, and 

 finally into the definitive body-cavity. 



The formation of the body-cavity in the Diplopoda seems to resemble that 

 in Moina. In this form also the food-yolk lies in the primary body-cavity 

 (Vol. ii., p. 177). Cells which become detached from the mesoderm-bands are 

 disseminated through it, and consequently these must indisputably be con- 

 sidered as true mesoderm-cells. These cells later also assist in the formation 

 of the blood-tissue. A similar fate is probably reserved for the yolk-particles 

 remaining in the pseudocoele of the Muscidae. 



The formation of the heart in the Diplopoda is said also to be 



traceable to the 

 cells contained in 

 the yolk (?). These 

 become arranged in 

 the pseudocoele to 

 form a dorsal tube, 

 which at first is in- 

 completely closed, 

 but later becomes 

 complete. Regu- 

 larly-placed paired 

 apertures that are 

 retained in this 

 tube represent the 

 ostia. In each 

 double segment of 

 the Diplopoda two 

 pairs of ostia de- 

 velop. In the same 

 way, each double 

 segment possesses 

 two pairs of arte- 

 ries, which leave 

 the heart ventrally 

 and run direct into 



Pig. 12S. — Portions of transverse sections through older em- 

 bryos of Geophilus ferrugineus (after Sograff). The sections 

 are made through the posterior part of the body, d, yolk- 

 mass with yolk-cclls ; dm, dorsal muscles ; fk, the fat-body ; 

 fl, alary muscles of the heart ; g, rudiment of the genital 

 glands ; h, the paired rudiment of the heart ; m, musculature ; 

 mil, enteron ; mes, mesodermal covering of the intestine ; 

 mp, Malpighian vessels. 



