234 bulletin: museum of comparative zoology. 



There are many places where one seems to see the free ending of 

 neurofibrillae (Figs. 14, Plate 3, 26, Plate 4). Such appearances, 

 however, might easily result from the shaving off of a portion of a 

 terminal structure in sectioning. 



B. In Maculae acusticae. 



It has been decidedly more difficult to obtain material satisfactory 

 for the determination of conditions in the sensory areas of the lagena, 

 sacculus, and utriculus, than in the ampullae. The wall of the ear 

 sac is considerably thinner in these regions than in the ampullae, the 

 sense cells being considerably shorter than those of the cristae acusticae. 

 The basement membrane is much thinner in the maculae than in the 

 cristae and in the non-sensory areas of the ear, and is further weakened 

 by the numerous perforations made by the penetrating nerve fibres 

 which supply the sense cells. As a consequence of this greater delicacy 

 of the wall of the ear sac in the region of the maculae acusticae, it 

 turned out that in many series in which the cristae acusticae showed 

 good impregnation the maculae were so shrivelled by the action of the 

 ammoniacal solution of silver oxide as to render them of no value. 

 The cases in which good impregnation has been secured and his- 

 tological relations have not been badly disturbed are much rarer 

 therefore in the maculae than in the cristae acusticae. Because of 

 the distortion of the non-nervous tissues, there was only a single series 

 among those in which all the nervous substance seemed to have been 

 impregnated where it has been possible to make use of the material 

 for the study of the maculae. I have obtained a number of series, 

 however, the general histological conditions of which are good, in 

 which there is an occasional impregnation of nerve fibres. 



In the maculae, as in the cristae, there is, between the supporting 

 cells and the sense cells, a stratum rich in nervous material, corre- 

 sponding to the so-called zone of plexus formation in the cristae. The 

 space between the sensory epithelium and the supporting cells is 

 considerably less in the maculae than in the cristae, and this nerve 

 plexus is therefore much less in thickness than in the cristae. I 

 have not found any cases of anastomosing fibres in this zone in the 

 maculae, but I have found many places where there was an interlacing 

 of fibres. Cases of such entanglements of fibres are represented in 

 Figures 29, 30, 32, 34, 35, 36 (Plate 5). 



I have not found structures in the maculae that I have been able 

 to regard as identical with the terminal expansions (calyces) which I 

 have described in the cristae, though giant fibres are abundant. In- 



