oral cirri of siluroids and origin op the head in vertebrates. 3 



Technique. 



The models have been made after the well-known method of Born, 

 but with certain additions to the technique. The heads of the small 

 fish were decalcified in picric acid, stained with alum carmine, and 

 subsequently with bleu de Lyon. Camera drawings were made on 

 ordinary tracing paper and then rolled in with the wax to make the 

 plates. I used the cheap impure wax with a low melting point of 

 the kind used, I am told, by printers. A large rectangular museum 

 bottle proved the best table on which to cut out the plates. 



After reaching a certain size the models became extremely difficult 

 to handle and it was necessary to find some method of strengthening 

 them. I decided to electroplate them. The parts were wired together 

 and then brushed with a suitable kind of blacklead. Then by applying 

 in the copper sulphate bath, a current up to 5 or 10 amperes, according 

 to the size of the model, a deposit of copper of sufficient solidity was 

 formed in a few hours. 



Subsequently they were painted and photographed. For opportunity 

 of carrying out these operations I am indebted to the Physical 

 Department of the Owens College. 



By subsequent calculation I find that the models are an appreciable 

 fraction too long in comparsion with the breadth, but that does not 

 detract to any great extent from their value. The wax plates must be 

 made considerably thinner than the calculated thickness, but how 

 much thinner depends on the "personal equation." 



On the occurrence op oral cirri. 



Oral cirri, barbels, barbules or tentacles occur in many fish, and 

 form one of the characters diagnostic of the Siluroids (Nematognathi), 

 in which they occur throughout, with the apparent exception of 

 Plecostomus. Much information on them can be gained from systematic 

 Avorks, especially from Giinther's Catalogue of Fishes, where the 

 subject is treated from the systematist's point of view. 



True barbels do not grow out indefinitely, but only with certain 

 morphological relationships, and the maximum number in the Craniata 

 is 6, or perhaps 7 pairs, which I term nasal, premaxillary, maxillary, 

 •coronoid, mental (and extramental) and submandibular. 



I attempted to draw up a list shewing the occurrence of the 



