38 PART I. GENERAL ACCOUNT 



The number of toothed bristles apparently gradually increases throughout 

 life thanks to the appearance of new ones deep in the epidermis along the 

 front edge of the girdles. Each bristle is formed inside a single cell. First, next 

 to the nucleus appears a round inclusion, which then grows bigger, gradually 

 taking on the shape of the toothed head. The inner end of such a young head 

 is pointed and there is no stalk. The head lies within a large vacuole. The 

 enveloping cell grows larger and soon afterwards forms a tight mantle pro- 

 tecting the sharp teeth of the head. Then, in the same way, the cell forms the 

 stalk too, so that the bristle gradually grows. Finally the head penetrates the 

 cuticle and emerges as a toothed platelet on the external surface of the girdle 

 (Ivanov, 1960a). 



The cell which forms the bristle remains at its base in the capacity of basal 

 attachment cell and tonofibrillae appear within it. Later this cell may de- 

 generate to a greater or lesser degree leaving behind the bundle of tono- 

 fibrillae which may look somewhat like muscle fibres (Fig. 26). 



The basement membrane 

 The basement membrane is always well developed. This thin structureless 

 supporting membrane, underlying the epidermis, in appropriate places 

 unites with other limiting membranes, attaching organs and tissues to the 

 epithelium above; instances may be found in the fascia of the mesentery of 

 the mesosoma and metasoma. 



The multicellular epidermal glands 



Apart from the single-celled glands mentioned above, all pogonophores 

 have multicellular glands of cutaneous origin entering into the composition 

 of the epidermis and sticking down into the coelom. Like the scattered gland 

 cells they certainly secrete tube material. [For this reason Ivanov refers to 

 them as tubiparous or tube-forming glands. The usual rule for the English 

 nomenclature of anatomical features demands, however, that an organ should 

 not be named for its known (or supposed) function, but from its appearance, 

 topography or anatomy. In this edition, therefore, these glands are termed 

 globular or pyriform glands according to their shape, or collectively as flask- 

 shaped glands: the distinction may or may not be valid — D.B.C.]. Two 

 categories may be distinguished : the globular glands lying in the coelom of 

 the mesosoma and metasoma, and the pyriform glands located in the coleomic 

 cavity of the adhesive papillae. There is no fundamental distinction to be 

 drawn between them (Ivanov, 1960a). 



These large flask-shaped glands with longer or shorter multicellular ducts 



