ORTHOPTEROIDEA (PANORTHOPTERA) 239 



The epineural sinus, which appears early in embryonic development 

 between the germ band and the yolk, is bounded dorsally by the provi- 

 sional dorsal closure in Locusta (Fig. 152), in Stenobothrus, and probably 

 in some other primitive insects, although in most of the pterygotes it 

 is open dorsally. With the growth of the embryo the sinus becomes 

 enlarged and forms the definitive body cavity, the haemocoele. 



The heart, or dorsal vessel, is formed from the cardioblasts, differ- 

 entiated in the 112-hour stage as two strings of single large rounded cells 

 lying on the dorsolateral border of the myoblast and extending through 

 the thorax and abdomen. With further development the cardioblasts 

 move toward the middorsal Hue and come to lie beneath the first lateral 

 blood sinus. At the same time they become crescent-shaped, with the 

 concave surface facing upward. The middorsal sinus in the posterior 



h 



muG 



Fig. 162. — Locusta. Cross section of heart (h) five days after blastokinesis. (cbl) Cardio- 

 blasts. (/) Fat. {mus) Muscle, {pc) Pericardial cells, (pd) Pericardial diaphragm. 



region of the abdomen at the time of blastokinesis is bounded dorsally 

 by the epidermis, ventrally by the provisional mesoderm wall of the mid- 

 gut, and laterally by somatic mesoderm. The cardioblasts lie dorso- 

 laterally close to the epidermis. Inside the sinus a few blood cells 

 may be seen (Fig. 159). The dorsal portion of the somatic mesoderm 

 mass (Figs. 159, 162) completely separates from the ventral part, becomes 

 membranous, and acquires a connection with the body wall by means 

 of fan-shaped processes. The dorsal membrane finally gives rise to 

 intersegmentally placed suspensory muscles of the heart, and the ventral 

 membrane to the pericardial diaphragm (Fig. 159). With the fusion 

 of the cardioblasts the heart is provided with a wall of its own. The 

 cephahc aorta develops from the internal walls of the dorsorostral and 

 dorsoanal pouches of the antennary coelomic sacs, the anterior portion 

 forming the blood-distributing apparatus, or pulsatile vesicle; the pos- 

 terior portion, the aorta proper. 



Three kinds of temporary embryonic blood sinuses are formed in 

 Locusta rnigratoria: lateral blood sinuses, dorsal blood sinuses, and the 

 circumintestinal blood sinus. Two pairs of lateral blood sinuses are 



