No. I.] THE SENSORY CLUBS. 293 



endoderm origin of its axis is a fibrous cord which penetrates 

 the thickness of the pad and joins the supporting layer of the 

 club to that of the bell-margin. 



Careful study of the figures and descriptions of the marginal 

 sense organs of the Narcomedusae and Trachomedusae which 

 are given by the Hertwigs will show that while the sensory 

 club'^of Laodice is much simpler than any of them, it is never- 

 theless essentially like them in structure and in all its ana- 

 tomical relations, and that it corresponds to an incipient stage 

 in their development before the endodermal axis loses its con- 

 nection with the endoderm of the bell-margin and acquires 

 concretions. 



The cordyli of Laodice have long been known, and we have 

 seen that Haeckel suggests that they may possibly be organs 

 of some special sense. We have therefore to inquire why 

 their agreement with the sensory clubs of the Trachylinae has 

 escaped notice. 



The most conspicuous feature in the structure of these clubs, 

 in the Trachylinae, is the presence of solid concretions or 

 crystals ; they are universally regarded as hearing organs, 

 and this interpretation derives most of its support from the 

 presence of these heavy bodies or " otoliths." It is only natural 

 for those who hold this opinion to assume that organs without 

 "Otoliths " cannot be ears, and that the cordyli of Laodice must 

 therefore belong to a different category from the "auditory 

 clubs and vesicles " of the Trachylinae. 



Examination of the evidence that these are hearing organs 

 is therefore in place. This opinion, which was not new when 

 the memoir of the Hertwigs appeared in 1878, is now regarded 

 as firmly established by their researches. 



In the second part of their memoir they introduce the subject 

 in the following words : — 



"In our morphological description we have hitherto spoken 

 of hearing organs, of auditory cells, and of otoliths without 

 examining the ground for the use of these terms, and we shall 

 now make good this omission by a comprehensive discussion 

 of the physiological significance of the organs of which we 

 have described the anatomy." 



