OBTHOPTEROIDEA {PANORTHOPTERA) 233 



medially, the median extension forming the ventral diaphragm. In 

 the 94-hour stage a deep furrow develops in the lateral coelomic wall 

 at the junction of the dorsorostral with the ventral pouch (Fig. 156), 

 which deepens and eventually separates the dorsal from the ventral 

 coelom. The ventral coelom gives rise to the leg musculature. At 

 the same time, the dorsal coelomic portion (both rostral and anal) is 

 divided by a horizontal partition into upper (dorsal) and lower (ventral) 

 halves. Soon the intersegmental partitions between the upper portions 

 of the dorsal pouches of the coelomic sacs disappear, with the result that 

 there are formed two continuous lateral tubes extending from the first 

 thoracic to the ninth abdominal segment. The somatic mesoderm 

 thickens and forms the so-called "myoblast plate" whose dorsal edge 

 contains cardioblasts (compare Fig. 160). The central part becomes 

 fatty tissue except the uppermost end which forms for a time the wall 



coel.l 



Fig. 156.— LocMsia. Cross section of distal and of second thoracic segment showing 

 ventrolateral furrow in coelomic wall, {am) Amnion, {coel) (1) Dorsorostral, (3) ventral 

 pouch of coelomic sac. {dc) Provisional dorsal closure, {eel) Ectoderm, {mes) Median 

 mesoderm, {sin) First lateral blood sinus. 



of the middorsal blood sinus. After completion of the heart it gives out 

 cells that form the pericardial cells. The upper portion of the myoblast 

 plate forms the dorsal suspensory muscles of the heart; the inner layer, 

 the pericardial septum. The median walls of the upper portion of the 

 dorsal pouch form fatty tissue in the thorax and in the first, eighth, and 

 ninth abdominal segments. In the second to tenth abdominal segments 

 it forms the gonads as well. As for the lower portion of the dorsal 

 coelomic pouch, its lateral walls form the vertical muscles of the body wall, 

 and the median walls form fatty tissue. 



The difference between the origin of the coelomic cavities of the first 

 abdominal segment and that of the following ones has already been 

 described. At the 75-hour stage (Fig. 152) there are 11 pairs of coelomic 

 cavities in the abdomen, of which the first 10 show a division into three 

 portions as in the thorax. The last, or eleventh, abdominal coelomic sac 

 (Figs. 152, 157) does not show the triple division. It disappears before 

 the 112-hour stage. It consists of a pair of long narrow sacs which run 

 dorsally along the proctodaeum. They will form the musculature of 

 the cerci, of the hind-gut, and of some fatty tissue. The further develop- 



