THE LATERAL SENSE ORGANS OF ELASMOBRANCHS. 473 



that the gelatinous contents are produced by the activity of the lining cells of the 

 canals, and have the function of protecting the sensory epithelia, and of affording a 

 means of transmitting stimuli. 



Minckert (1901) and Coggi (1902) both worked at the development of the 

 ampullae — the former in Spinax niger, the latter in Torpedo, Rata, Mustelus, and 

 Pristiurus. Coggi points out that, since the lateral sensory apparatus appears while 

 the ectoderm still consists of a single layer, Balfour's statement as to the mucous 

 layer only taking part in its formation is incorrect. 



Alms's memoir (1902) on the Sensory Canals, Eye-Muscles, and Cranial Nerves 

 of Mustelus Isevis was the result of work undertaken primarily in order to investigate 

 the innervation of the ampullae and the lateral canal, and during the course of it the 

 author became confirmed in his previous impression that the ampullae of Selachians 

 are homologous with the terminal buds of Ganoids and Teleosts and the nerve-sacs 

 of Acipenser rather than with the pit-organs of those fishes. This view is criticised 

 by Johnston (1902) as being " wholly unsound and likely to lead to further 

 difficulties." 



The work of Mrs Hawkes (1906) on The Cranial and Spinal Nerves of 

 Chlamydoselachus anguineus touches only indirectly on the ampullae, the chief 

 points of interest in connection with which are their diffuse arrangement and 

 the absence of a mandibular group. 



Further researches on the development of the Lorenzinian ampullae were carried 

 out by Brohmer (1908) in Spinax embryos. He claims that his work confirms and 

 supplements that of Minckert, but he makes no mention of the more recent and 

 very complete work of Coggi, with whose results as regards the stages in develop- 

 ment observed, and as to the non-simultaneous appearance of the ampullae, Brohmer's 

 was nevertheless in agreement. The very confusing nomenclature adopted by 

 Brohmer for the ampullary groups might have been avoided had he observed 

 Coggi's remark that " the most rational way to classify the ampullae is according 

 to their innervation, especially since this accords with the facts of development." 



3. General Characters and Distribution of the Ampullary Canals. 



The species of Raia investigated in the course of these researches were seven in 

 number, viz. R. batis, R. fullonica, R. radiata, R. circularis, R. clavata, R. micro- 

 cellata, and R. maculata, the nomenclature adopted being that used by Day, in his 

 Fishes of Great Britain and Ireland. Of these the first four were obtained in Edin- 

 burgh from the Firth of Forth, while the specimens of the last three species were 

 obtained in Brixham fish-market, on the south coast of England. 



The results of the observations made have been summarised so that an account 

 of the ampullary system could be given applicable to the genus as a whole ; sub- 

 sequently each species is reviewed in turn and the distinguishing features pointed 



