CHAPTER 10 



Embryological Development 



At the time of writing only two publications have presented original 

 observations on the embryology of Pogonophora. In 1957 I wrote an 

 account of the embryological stages of Siboglinum caulleryi with a few 

 observations on Oligobrachia dogieli (Ivanov, 1957b). Almost simultaneously 

 the work of Jagersten appeared, in which he gave an account of the late 

 embryo of a species of Siboglinum. Embryos of another 

 species were also found in 1957 by E. C. Southward and 

 A. J. Southward, who managed to observe them alive 

 for a short time. Unfortunately the results of these 

 observations remain unpublished. This chapter there- 

 fore is based largely upon my own observations, many 

 of which must perforce be of a preliminary nature and 

 will probably be corrected and extended in the future. 



The clutch of eggs 



A female pogonophore lays her eggs in the anterior 

 part of her own tube, in whose protection they remain 

 throughout embryological development. Clutches of eggs 

 have been studied in four species of Siboglinum, including 

 S. caulleryi and S. inerme, and in Oligobrachia dogieli 

 and Lamellisabella zachsi, i.e. in representatives of both 

 orders. In Siboglinum caulleryi a clutch consists of 10-30 

 eggs lying in a single row one behind the other in the tube 

 in front of the animal which has laid them (Fig. 70). 

 Sometimes the tentacle of the female may be seen twist- 

 ing between the eggs. In Oligobrachia dogieli a clutch of 

 42 eggs was once observed, also disposed in a single row, 

 and a second clutch consisted of 45 embryos. 



The eggs lie in the tube one behind the other and are 

 not stuck together by any form of cement. In those 

 species in which the eggs are elongated {Siboglinum) they 

 are all orientated in the same way in the tube — front 



'■$: 



Fig. 70. Eggs of Siboglinum caulleryi, lying in the tube. (After Ivanov, 1957b.) 



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