CHAPTER 9 

 The Reproductive System 



All the information we have so far amassed about the organization of the 

 Pogonophora suggests that they possess only sexual means of reproduction. 

 The supposed presence of external budding in Siboglinum (Caullery, 1944) 

 and the more recent supposition of internal budding (Jagersten, 1956) have 

 received no confirmation. The "internal buds" reported by Jagersten in 

 S. ekmani appear to be artifacts resulting from one part of the trunk con- 

 tracting on fixation and becoming enveloped by another part rolling around it. 



The Pogonophora have separate sexes but there is no pronounced external 

 sexual dimorphism. The sexes are distinguished externally only by the 

 position of the genital aperture (p. 20). 



The most characteristic features of the reproductive system of the 

 Pogonophora are as follows: 



1 . They possess a single pair of gonads lying in the metasomal segment — 

 in the hind half of the trunk in the male and in the front half in the female. 



2. The single pair of metasomal coelomoducts are transformed into 

 gonoducts (Ivanov, 1955a). 



The male reproductive system 



The male reproductive organs have been studied in Polybrachia, Lamelli- 

 sabella and, in part, in Siboglinum (Ivanov, 1958a). They consist of a pair of 

 seminiferous sacs or testes and a pair of tubular spermducts. 



The testes or sperm sacs 



The testes stretch from the level of the zone of thickened papillae to the 

 hind end of the body. They consist of rather broad canals immediately 

 adjoining the dorsal part of the mesentery, which in places forms, with the 

 dorsal vessel, a vertical partition between them (Fig. 60). The testes are 

 separated from the ventral vessel by a considerable distance, but anteriorly 

 they are so large that they extend the whole distance between the dorsal and 

 the ventral body walls. 



The walls of these sacs consist of a ciliated epithelium which appears to be 

 a continuation of the splanchnopleura that covers the mesentery and the 

 dorsal vessel. Correspondingly the basement membrane too of the wall of the 



90 



