10. EMBRYOLOGICAL DEVELOPMENT 



111 



Fig. 77. Diagrams of Siboglinum caulleryi illustrating: A -the detachment of the coelomic sacs, 

 and, В - the first stage of segmentation. 



a - cells of the anterior ectodermal girdle ; с a - anterior ciliary girdle ; сое I, сое II and сое III - 

 first, second and third coelomic sacs; di - diaphragm; ec - ectoderm; en - endoderm; mts -meta- 

 soma. (After Ivanov, 1957b.) 



The anterior and lateral coelomic pouches 

 then become separated and the latter become 

 pinched across to form the second and third 

 coelomic sacs. The coelomic pouches are thus 

 formed in a similar way to that found in 

 Saccoglossus pusillus (Enteropneusta), whose 

 egg is also rich in yolk (Fig. 78) (Davis, 

 1908). 



Fig. 78. Formation of the coelomic sacs in Saccoglossus 

 pusillus (Enteropneusta.) 



ar - archenteron ; сое 7-protocoele; сое II - mesocoele ; 

 сое III - metacoele. (After Davis, 1908, from Korschelt.) 



coel 



