BEANCHIAL SENSE ORGANS OP ICHTHTOPSIDA. 213 



paper on this point seems to me to meet the objectionable points so 

 successfully that further criticism is unnecessary. 



In connection with this table the reader would do well to consult 

 the three diagrammatic figures (figs. 43, 46, 51). The same results 

 are there shown. Fig. 43 is a diagrammatic horizontal section through 

 the various sense organs and ganglia, and with fig. 45, which is a side 

 view of the same structures, shows the primitive condition. Fig. 45 

 shows the primitive position of these sense organs over the gill-clefts : 

 in it, for simplicity, the post-branchial nerves are left out ; but in 

 fig. 46 these and the pree-branohial nerves are shown. The closed 

 gill-clefts are also given, with the absorbed branches, in dotted lines. 

 Finally, fig. 51 is meant to show the adult condition of the supra- 

 branchial nerves, which are very diagrammatically given in fig. 46. 



The Relations op the Branchial Sense Organs to the "Seiten- 



ORGANe" OP CAPITELLIim 



Eisig 1 first suggested that these two sets of organs were homologous. 

 Since then no one has added anything to the grounds for this 

 homology furnished by Eisig. Until now it may truly be said that we 

 knew nothing of the morphology of these branchial sense organs of 

 Vertebrates. Now we do know a little, and this appears to me to place 

 the homology of the " Seitenorgane " of Capitellids with the branchial 

 sense organs in a very doubtful light. We have seen that primitively 

 these branchial sense organs are not found in all segments of the 

 body, but are limited to the head, that they have special ganglia, and 

 are special sense organs of the gill-clefts. 



In all these points they differ from the Seitenorgane of the Capitel- 

 lidse, and, interesting and important as Eisig's researches are, we must 

 at present, I think, hesitate to accept the proposed homology. 



Physiology op the Branchial Sense Organs. 

 Of this we really know nothing. Leydig, who has the honour of 

 having first described these sense organs, thought they were organs of 

 a sixth sense. By others they have been regarded as touch organs, 

 and as organs for testing the water breathed. Lastly, Mayser 2 

 suggested that they were a low form of auditory organ, and Emery 3 



1 Eisig, " Die Seitenorgane unci beckerformigen Organe cler Capitelliden," Mittheil. a. d. 

 Zool. Station zu Neapel,' Bd. i. 



2 Mayser, " Studien liber das Gebirn der Knocbenfiscbe, ' Zeit. f, wiss. Zool.,' vol. xxxvii 

 1881. 



3 Emery, " Fierasfer," p. 48, ' Fauna and Flora of the Bay of Naples,' 



