739 



whicli, — as previously — it is se|terated by the jugular veiu and 

 (lie facial nerve. 



The corpus of the bladder, with its long neuroinast, is visible on 

 the anterior 21 sections. The excretory duct falls in the following 

 29 sections. The nenroniast thus nearly constitutes half the lengtli 

 of the organ, and is much larger llian in the lateral line system 

 organs of the skin. Round the corpus one sees the mesenchym in 

 more compact formalion, the first stage of a connective tissue cap- 

 sule. The excretory duel, immediately posterior to the corpus, shows 

 a dilferent construction than further caudalwards. 



Fig. 2a. Cross section through the otic Fig. 2b shows the spiracular organ 



region of the skull and the anterior wall under high power. Its contents, mucus 



of the spiracle, from a 98 m.m. long (stained blue in section) are seen as thin 



embryo of Acanthias vulgaris. striations. 



On the first 5 sections behind the corpus, the medial wall of the 

 duct is thicUened, as the result of the proliferation of the outer 

 layer of epithelium cells. Here the oval lumen is wider than in 

 other places. The longitudinal axis of the oval is more or less twice 

 as long as in the corpus. On the following 24 sections this lumen 

 continually decreases,' the wall consisting of two layers of cells. 

 Those of the inner layer are very Hat, those of the outer layer 

 may be called cubic. 



It is of importance that the corpus of the sense organ bladder 

 and the proximal part (5 sections) of the duct, should be filled with 

 mucus, which in this stage (and later) allows itself to be stained 

 blue, just as in the ampullary and canal organs of the lateral line 

 .system. In the distal pai'l of the duct (24 sections) the mucus is 

 present in lesser quantity. 



