BRANCHIAL SENSE ORGANS IN ICHTHYOPSIDA. ite 
first there is no nerve in connection with the developing 
sensory thickening. 
This is right so far as its growing point is concerned, for 
there the nerve has not developed. 
But, as Van Wijhe has pointed out, it is not really the case 
so far as relates to entire absence of nerve in connection with 
the sensory thickening, and, further, the connection between 
sense thickening and nerve is best made out in early stages, 
and is afterwards not so easy to trace. 
Van Wijhe himself, though he has given a true, accurate, 
but somewhat incomplete account of the development of these 
supra-branchial branches to the sense organs, cannot be said 
to have solved the difficulty under discussion. He has rather 
ignored it, and though possessing the material for its solution 
has not mentioned the matter. It is very curious that, 
although he has figured the fusion of various ganglia with 
the skin, he has apparently not noticed that the supra- 
branchial branches grow in the various cases out of the various 
ganglia so fused, and therefore are in connection with 
their appropriate ganglia from the first. 
In fact the whole rationale of the formation of supra- 
branchial nerves is to be seen in the deploying of the branchial 
sense organs, and in the connection of these organs with the 
ganglionic centre by longer or shorter conducting fibres—the 
supra-branchial nerves. Originally the sense organs were 
restricted to one over each gill-cleft with an associated 
ganglion.’ This increased, and gave rise to two by division, 
and soon. This is the more certain when we remember that 
even in late stages, according to Malbranc,” the sense organs 
of Amphibia increase by division. I have myself noticed and 
recorded this mode of increase in embryonic Teleostei.* 
1 Beard, ‘“ Segmental Sense Organs and Associated Ganglia,” ‘ Zool. Anz.,’ 
192, 1885; also Froriep, “Ueber Anlagen von Sinnesorgane am Facialis, 
&e.,” ‘Archiv fiir Anat. und Physiol.,’ 1885. 
2 Malbranc, “ Von der Seitenlinie u. ihren Sinnesorganen bei Amphibien,” 
‘Zeit. f. wiss. Zool.’ vol. xxvi, 1876. 
3 Beard, ‘Segmental Sense Organs of Lateral Line,” ‘ Zool. Anzeiger,’ 
Nos. 161, 162, 1884, 
