MYRIAPODA 



393 



position. In a manner similar to the formation of the aorta, the ventral 

 blood vessel (epineural vessel) is formed; i.e., mesally the ventral margins 

 of the coelomic sacs unite, leaving a small canal between them. Thus the 

 slender tubular blood vessel composed of contractile fibers is formed. 

 The lateral transverse vessels, intersegmental in position, arise inde- 

 pendently by the meeting of two adjacent coelomic sacs of the same side 

 in the same manner as the formation of but not as evaginations from the 

 epineural vessel. 



The dorsal growth of the dorsal limb (Fig. 348, coel 1) of the coelomic 

 sac which has carried the cardioblasts {cbl) into their definitive position 



dl 



Im oind xl I 



Fig. 349. — Scolopendra. Cross section (schematic), (aim) Heart wing muscle, (dl) 

 Dorsal ligament, (dr) Dorsal nerve, (ep) Epidermis. (/) Fat. (g. cod) Genital coelome. 

 (h) Heart. (Im) Longitudinal splanchnic muscle, (mge) Midgut epithelium, (mus) 

 Muscle, ipm) Paricardial membrane, {splm) Splanchnic mesoderm, (tp) Tunica peri- 

 tonealis. {xl) Transverse splanchnic muscle. 



has brought the mediodorsal parts of the sacs of the two sides into contact 

 with each other in the form of a pair of contiguous flat tubes (Fig. 349, 

 g. coel), constituting the genital anlagen. The somatic (dorsal) wall of 

 this anlage is continued laterally in the somatic wall of the original 

 coelomic sac, from which later cells are given off for the formation of the 

 thin pericardial membrane (Fig. 349, pm). This membrane is split near 

 the heart into two lamellae, the lower one fusing with the heart wall, the 

 upper (dorsal) one continuing on the side of the heart and attaching itself 

 to the dorsal body wall (Fig. 349), forming a dorsal ligament (dl). The 

 visceral wall of the coelomic sac will form the muscles and the very thin 

 peritoneum of the gut (Fig. 349, tp, xl, Im). Only a small part of the cells 

 of the lateral somatic wall of the coelomic sac enters into the formation 

 of the pericardial membrane; the remainder will give rise to the wing 

 heart muscles (Fig. 349, aim). The wing heart muscles (aim) and 

 the pericardial membrane (pm) together form the pericardial septum. 

 Dorsad of this septum is the pericardial chamber in which the dorsal 



