286 



PART II. SYSTEMATIC ACCOUNT 



On the dorsal side of the body these cells form a sort of primitive dorsal 

 shield, but more often they extend -right round onto the ventral side as well 

 (Fig. СС133Я). 



To gain a clear idea of the size and proportions of the various parts of the 

 body I measured 25 individuals. The hind part of the animal, however, was 

 unfortunately missing in most of the animals and only in three individuals 

 was there a more or less complete postannular region. The sizes of the parts 

 of the body vary as follows (dimensions given in millimetres) : 



Length of tentacle 4-5-8-8 



Length of the fore-part of the body 1-8 - 2-9 



Breadth of the mesosoma 0-16-0-27 



Length of the metameric part 8-0 -12-5 



Length of the preannular section up to 84 



Length of the postannular part probably not less than 30. 



The overall length of the body, including the tentacle, may reach 125 mm. 



The spermatophores of Siboglinum subligatum are very characteristic. They 

 are very thin and shaped like elongated spindles or cigars. One end of the 



spermatophore is drawn out into the base of 

 the filament, the other forms a very thin and 

 rather long "tail-piece". The sperm are ar- 

 ranged parallel to one another (Fig. DD 133^4). 

 The spermatophores are 0-3-0-35 mm long, 

 not counting the "tail-piece", and the greatest 

 breadth is 0-02-0-03 mm. 



The white lustrous flexible thick-walled 

 tube is unsegmented and ringed. The mem- 

 branous transparent front end of the tube has 



0.05 



MM 



в 





■ 



0.3 



MM 



\ л 



Fig. DD133. Siboglinum subligatum: .4 - spermatophore ; 

 B-D - successive parts of the tube. 



