BRANCHIAL SENSE ORGANS IN ICHTHYOPSIDA. a7 
mobranchs. The branchial sense organs are those sense organs 
which have usually been called organs of the lateral line, and 
were formerly called ‘ segmental sense organs” by me. The 
name “organs of the lateral line” is bad, because it chiefly refers 
to those sense organs along the lateral line of the trunk, which 
morphologically form only a small portion of the sense organs. 
I have myself seen reason to reject the name segmental sense 
organs, because although originally they are segmental, and in 
later life may occur one in each segment of the trunk, still at 
first they are confined to one region only of the 
body, the gill-bearing region, and only extend into the 
trunk much later. Originally they are seated one above each 
gill cleft or over the site of each cleft, and may, therefore, be 
called branchial sense organs.! 
The so-called ganglia of the posterior roots of the cranial 
nerves arise in connection with them, and must be regarded as 
originally special ganglia of these sense organs.? 
One general conclusion may be referred to here, and that is, 
that at present we are acquainted with no iuverte- 
brate nervous system which is built upon the same 
plan as that of Vertebrates. 
The matter will be discussed later on, and I only refer to it 
here in order that from the outset the branchial sense organs 
may be raised from their present position of neglect and 
obscurity, and may be given that important morphological (and 
physiological) place which their relationships to the gill clefts 
on the one hand, and to the ganglia of the posterior roots of 
cranial nerves on the other, most certainly entitle them to. 
Unlike many previous observers, I have found that it is 
absolutely impossible to study the branchial sense organs of 
fishes without at the same time dealing with the posterior roots 
‘ Beard, “Cranial Ganglia and Segmental Sense Organs,” ‘Zool. Anzeig.,’ 
192, 1885 ; also Froriep, ‘“‘ Ueber Anlagen von Sinnesorgane am Faciales, &c.,” 
‘ Archiv fiir Anat. und Physiol.,’? 1885. 
? Beard, op. cit.; Froriep, op. cit.; and Spencer, “ Notes on the Early 
Development of Rana temporaria,” ‘Quart. Journ. Micro. Sci.,’ Supple- 
ment, July, 1885. 
VOL. XXVI.—NEW SER, G 
