114 



PART I. GENERAL ACCOUNT 



A little later the bristles pierce through the epidermis one by one and stick 

 out above the body surface. The bristle sac then fuses with the epidermis and 

 spreads out (Fig. S\B). There are no muscle fibres associated with the bristle. 



The last known stage of development (Fig. 82) has been studied in a few 

 embryos from a single batch in Siboglinum caulleryi. Externally these 

 embryos already resemble the adult but are sharply distinguished by the 



Fig. 80. Transverse sections through a late embryo of Oligobrachia dogieli: A- section at the level 

 of the tentacular buds ; В - section through the metasoma. 



сое - coelmoic canal of tentacle ; сое I - protocoele ; сое HI - metacoele ; e с - ectoderm ; en - endo- 

 derm ; gc - gastrocoele ; td - first tentacle ; ts - bud of second tentacle ; vv - ventral blood vessel. 

 (After Ivanov, 1957b.) 



