AND THE CRISTA SPIRALIS OF THE COCHLEA. 69 



The two vertical sections represented in figures 20 and 21 give a true picture 

 of these conditions. The first is from a pig embryo of 190 mm., the second from 

 a young dog of about 4 months. Compared with figure 16, they show that the 

 teeth (t) and the interdental epithelial sheets (ep) become much longer, as seen in 

 figure 20. The teeth enlarge superficially, and by compression the intermediary 

 cytoplasmic sheets are mechanically reduced to a kind of membrane which remains 

 in direct continuity with the superficial epithelial mosaic (mcr). This latter is 

 stained a little darker than the thin cytoplasmic sheets. In the depth the teeth 

 keep their previous size or enlarge very little between the nuclear portions of the 

 sheets, but from there their transverse diameter rapidly increases toward the surface 

 and toward the depth. On the contrary, the epithelial bands become thinner in 

 both these two directions. At their base the teeth with their cell prolongations 

 merge with the subjacent connective-tissue. 



Figure 21 shows the different layers of the adult crista spiralis: 



1. Superficially the membrana tectoria (mt). 



2. The cytoplasmic mosaic (mcr) beneath the former. 



3. The epithelio-connective layer formed by the teeth (/) and the interdental 



epithelial sheets (ep). 



4. A subepithelial connective layer formed by a collagenous substance, including 



occasional spaces with stellate cells and a system of canals with cell prolon- 

 gations (pr). These latter are visible in length, in great number reaching 

 the surface of the teeth. The teeth of Huschke are real extensions of this 

 subepithelial layer. 



5. A deep layer where the fundamental substance is less abundant and the cells 



with their prolongations more numerous. 



6. A periosteal membrane (per), which later will undergo ossification and form 



a bone lamella separating the crista spiralis from the subjacent nerve-fibers 

 (ner). 



My description of the connective tissue is for the most part similar to that of 

 Vernieuwe (1905). 



Tangential sections of the adult stage of the crista spiralis are represented by 

 figures 22 and 23. The first is from a pig embryo of 190 mm., the second from an 

 adult bat (Vcspertiliu fu^-us) . They show three different planes in succession. The 

 first and most superficial is the mosaic (mcr), consisting of clear polygonal fields 

 separated by rather thin terminal bars (fig. 23), which in figure 22 are split longi- 

 tudinally and exhibit intercellular bridges. Figure 24 displays a similar veil from 

 the cochlea of a young dog, but within the polygonal fields one sees a dark circular 

 mass, a kind of plate which represents the attraction sphere (sph) formed by a cen- 

 tral corpuscle (cp), a small, clear medullary zone, and a larger dark cortical zone. 

 In the cochlea of the adult mouse I could notice the successive stages of division 

 of this dark layer into two smaller dark plates. It is an unexampled and surprising 

 process in the evolution of the sphere, the function of which in the cell completely 

 ceases after the last mitosis during the earliest stages of development. 



A second plane, cut by the razor a little more deeply, shows a system of dark 

 bands, granular and non-nuclear (pb), which become nuclear in the still deeper 



