214 JOHN BEAED. 



instituted a comparison between the auditory labyrinth and branchial 

 sense organs, and concluded that the two sets of organs have an 

 analogous function. That this is the case seems now very possible ; 

 that they are concerned in the perception of wave motion is obvious 

 enough from their structure. 



I have here shown, and Professor Froriep 1 has also come to the same 

 conclusion, that they are the special sense organs of the gill-clefts. 

 On this view we may assume that they give notice of impending- 

 danger to the gill-clefts, and so enable the latter to be closed. Of 

 course they were existent long before an operculum was developed in 

 any fish. 



After this demonstration that these sense organs stand in some 

 important relationship to the gill-clefts, it may reasonably be expected 

 that experimental evidence of their real nature will shortly be forth- 

 coming. Here a valuable field of research is open for the physiologist, 

 and a very important one too, for researches in it may lead to a better 

 knowledge of other Vertebrate sense organs, such as the nose and ear, 

 which appear to have been primitively of the same nature as these 

 branchial sense organs. 



If the researches recorded here should give any impulse to the 

 physiological study of these organs, they will have done a great deal ; 

 for in spite of the many brilliant researches on the structure of these 

 branchial sense organs, which have undoubtedly told us much about 

 their structure and distribution, we cannot till now be said to have 

 gained a clearer insight into their true nature than we possessed after 

 Leydig's researches. This honoured histologist and zoologist showed 

 that they were really sense organs, but there the matter has remained 

 for thirty-five years. 



My researches on the lateral line were commenced over two years 

 ago in Professor Semper's laboratory at Wurzburg. In consequence of 

 difficulties with the only material I then had, viz. embryos of 

 Teleostei, they led to very little result. Afterwards they were for a 

 time laid aside for other work. Although the results of the work in 

 Wurzburg were very barren, being made in what appeared to be a 

 dreary and empty field, still my gratitude is none the less due, and 

 is here expressed, to Professor Semper for his untiring advice and 

 assistance. 



1 This was stated by Professor Froriep and myself independently. 



