208 JOHN BEARD. 



what remarkable that Prof. Froriep should have failed to find rudiments 

 of such sense organs in connection with the Gasserian and ciliary 

 ganglia, and I cannot help expressing a firm conviction that such 

 rudiments exist at some stage or other in Mammalian development. 

 This conviction rests on a twofold basis — an a priori one, that in 

 Elasmobranchii the sense organs of the ciliary and Gasserian ganglia 

 are very well developed • and, secondly, on the discovery, of which I 

 hope soon to give a full account, that such rudiments occur, and are 

 very obvious in embryo chicks. They are in the chick especially obvious 

 in the cases of the ciliary and trigeminal segments, but they also occur 

 in the segments of the facial, glossopharyngeal, and vagus. 



Of course here, as in Mammalia, they disappear after the fish stage 

 has been passed through, but when they attain the maximum of their 

 development one could almost fancy, in studying them, that it was 

 an Elasmobranch embryo which was under examination, the state of 

 affairs in both cases being so alike that one can only marvel that these 

 rudiments have hitherto escaped notice in the chick. So much for the 

 present. 



The Nose and Ear as Branchial Sense Organs. 



In the preceding pages abundant evidence has, I think, been adduced 

 to show that the nose and ear are specialised branchial sense organs. 

 Whether they ever had gill-clefts in connection with them is a point 

 which, from the evidence at present at our disposal, we cannot decide, 

 and can only suspect that such was once the case from the relationship 

 of the other branchial sense organs to gill-clefts, and from the known 

 facts that certainly Vertebrates once possessed more clefts than at 

 present. At any rate, at present the thymus or thyroid of the nose 

 and ear, or their equivalents, have still to be found. 



The only zoologists who have suggested a different view of their 

 nature are Froriep and Blaue, who have suggested that the ear is a 

 gill-cleft. Apart from the evidence given in the preceding pages, 

 which is inconsistent with this view, one may reasonably ask that the 

 supporters of such a view shall give us more evidence than that afforded 

 by an epiblastic depression that an organ is a gill-cleft. 



In this matter the nose and ear stand on equal terms, and until we 

 have a few more of the structures which compose a gill-cleft and visceral 

 arch, such as arterial arch, cartilage, &c, assigned to them, we can 

 reasonably regard the matter with a certain amount of reserve. 



