ÔX THE DEVELOPMENT OF LIMULU8 LOXUISPIXA. 85 



laterul hulve.s of the first cœlomie cavity only are fürfed tof>ether and 

 not .-separated by a longitudinal «lit (figs. 16, 52). In later stages, 

 however, tlie walls of all the cœlomie cavities fuse tou'ether at two 

 lines, d(3rsal and ventral. Thus a tulje is formed (figs. 54-5G). The 

 tube, as in the case of spiders, has many lateral slits (ostia). as the Avail 

 does riot fuse together at the intersomitic lateral places. In the tube 

 some wandering mesoblast cells are enclosed. They are destined to 

 become Ijlood corpuscles. Probably all the blood corpuscles are formed 

 from these cells. 



As no cœlomie ca\ity is developed in the segments of the second, 

 third, and foiu'th appendages, tlie mesoblast of these segments plavs no 

 part in the formation of the wall of the d(jrsal circulatory vessel. The 

 first cadomic ca\ ity, ^vhich Ijelongs both to the cephalic segment and 

 t(j the segment of the first appendage, also does not take part in the 

 formation of the dorsal circulatory vessel, because the walls of its 

 two halves are fused together as stated above (fig. 17). 



When the dorsal vessel is not yet completely formed, the aortic 

 arches {(10. a.) are produced at the sides of the œsophagus (figs. 17, 

 45). A tubular lumen appears in the mesoblastic wall of the first 

 cœlomie cavity, where the somatopleur and splanchnopleur unite, 

 between the cœLjmic cavity and the œsophagus. The lumen is paired. 

 The lumina of the two sides unite into one and communicate with the 

 lumen of the d<jrsal circulatory vessel, at the posterior end of the blind 

 stomodieum (fig. 17). 



While the aortic arch is thus developing, a large unpaired blood 

 space (.s^ a.) appears Ijclow the entosternite {entost.) and around the 

 nerve cords ou the ventral median line (figs. 50-5:^, 56, 5(S, 68), 

 T'his is the sternal artery, which communicates anteriorly with the 

 aortic arches in later stao-es. 



o 



L can not but tliink that Kinu'slev is mistaken in reo'ard to the 



