MUSEUM OF COMTAItATIVK ZOOLOGY. 85 



papilla from the same region in Lepidogohins is given in Figure 2G. 

 Between Figures 24 and 26 there is considerably less difference than 

 may often be seen between sections of different papillaj'of the same 

 animal. Thus the sense cells proper (cl. sus.), which are very regular in 

 their arrangement in Figure 20, are quite irregular in Figure 24 ; but 

 Figure 23 agrees much more closely in this particular with Figure 26 

 than with Figure 24. Indeed, the difference is due to the position and 

 direction of the section, both arrangements being found on sections of 

 one and the same papilla at times. The cuticular spikes, so distinctly 

 seen on the sense cells in Figure 23, are much less distinct in any of 

 the Lepidogobius sections examined ; but they are only exceptionally 

 seen with such clearness in sections of the blind fish papillae. It will 

 be noticed that a considerable space {tt.) exists in Figure 26 between the 

 sensory cells and the underlying nuclei of the supporting cells, in which 

 there are no nuclei ; and that such a space does not appear, at least con- 

 spicuously, in either of the figures from Typhlogobius. This, however, 

 is not a difference of material significance, since in many sections of 

 the papillae of the blind fish such spaces do exist. In Figure 24, it 

 will be observed that a blood-vessel, va. sng. (the leader from which 

 has been misplaced in the engraving), penetrates far into the interior 

 of the papilla. A similar vessel is present in Figure 26, though it does 

 not extend quite so far into the base of the papilla, nor have I in any 

 case found it to do so in this species, though it is true I have not 

 examined as large a number of sections of Lepidogobius as of the blind 

 fish ; but the difference, if distinctive of the two forms, is nevertheless 

 insignificant. Neither as regards the mantle cells {cl. mt.), nor the rela- 

 tion of the papilla to the epidermis, — i. e. its extending entirely through 

 the thickness of it, — nor the way in which the nerve approaches and, 

 enters the papilla, nor the character of the immediately underlying sub- 

 epidermal tissue, is there the slightest characteristic difference to be 

 made out between the two species in such papillae as are represented 

 in Figures 24 and 26. 



In only one point a difference may possibly exist between them, 

 though I have not yet been able fully to satisfy myself of this. By 

 Figure 23 it will be seen that the papilla is wholly and deeply buried in 

 the epidermis, only a small pore (po.) communicating with the outer 

 world. The apparent bridge across the pore near the papilla is prob- 

 ably a point of contact merely, as adjacent sections show. The whole 

 appearance is as though the papilla had been withdrawn into the epi- 

 dermis ; for not only is the latter much thickened immediately around 



