186 MR. r. J. COLE ox THE STEUCTURE AND MORPHOLOGY OE 



Beavd (1888, 21), who at first combated Eisig's views, finally accepts them in the 

 following words (p. 21G) : — " Like Dr. Eisig I support, as the result of these researches, 

 Kleiuenherg's view of the homology of the spinal ganglia of Vertebrates, and the 

 parapodial ganglia of Annelids. But I go further, and say that what in the sense given 

 above may be called the cranial neural ganglia of Vertebrates, are also moi'phologically 

 equivalent to the parapodial ganglia of Annelids. I am also fully prepared now to 

 accept with Eisig the homology of the branchial sense organs of Vertebrates with 

 the Seitenoro-ane of Annelida." That the branchial sense organs, which are doubtless 

 more archaic structures than the lateral sense organs, and were perhaps, if not now, 

 primitively segmental, corresj)ond to the segmental sense organs of Annelids is most 

 probable, but w^e have already seen that the branchial sense organs are not the lateral 

 line organs, and hence Eisig's comparison must in the meantime lapse. 



Further opposition to the Annelidan homology is supplied by Wilson (1891, 225), who 

 opposes Eisig's views, and points out, what we now know to be true, that the Capitellidan 

 lateral sense organs have a totally different development to the lateral organs of Verte- 

 brates. Ayers (1892, 7), after insisting that the " auditory organs of Invertebrates are 

 not the forerunners or the ancestral forms of the vertebrate auditory organs " (p. 317), 

 remarks that " it is of course possible that other sense organs of the invertebrate body 

 have developed in the course of descent into the canal organs from which the vertebrate 

 ear arose." Mitrophanow (1893, 143) is very emphatic on the point. He maintains 

 that the lateral sense organs of Vertebrates have nothing in common with the lateral 

 organs described by Eisig in Capitellids, and states, what I have previously discussed, 

 that the former are not metaraeric (pp. 211-216) — a vital difference between the two 

 series of organs. Finally, Leydig (1S95, 128) and Locy (1895, 130) are somewhat in 

 favour of the comparison, the latter, however, Avhilst connecting vertebrate with inverte- 

 brate sense organs, considering the branchial sense organs, and not the lateral organs, 

 to be the homologues of the sensory papillae of Annelids. 



To sum up, there are two, to my mind fatal, objections to Leydig's and Eisig's views 

 that the segmental sense organs of Annelids are the direct homologues of the lateral 

 sense organs of Vertebrates. Before such a comparison can be said to hold good, 

 the most essential feature of the invertebrate organs, i. e. their metamerism, must be 

 satisfactorily established in their supposed homologues, the vertebrate lateral sense 

 organs. We have already seen that the latter are metameric only on the body, and 

 that this metamerism is purely secondary, whilst there is practically no evidence to show 

 that the vertebrate organs were primitively segmental. My second objection is based 

 on the palseontological fact that the vertebrate lateral line system is an extremely 

 archaic structure. It existed in the oldest fossil fishes known, i. e. in Silurian times. 

 If, therefore, we accept Dr. Eisig's homology, we must believe that the sense organs' of 

 the specialised Annelids have had an ancestral history equaUy archaic. This of course 

 is possible, but it is to my mind too improbable to base even a speculation upon, and 

 perhaps what shadoAV of possibility it has is removed by the fact that the Invertebrates 

 possessing lateral sense organs cannot be considered primitive forms. 



