446 HENRY C. TRACY 



around the labyrinth. He demonstrates the fact that the utric- 

 ulus does not send a diverticulum into the anterior bony capsule, 

 and that the caecum of the utriculus (Ridewood) or the 'bulbe 

 accessoire' (Breschet) is merely a three-sided thickening which 

 projects from the wall of the utriculus. 



Tysowski discusses at length the morphology of the dense 

 tissue and the channels in it which surround and connect the 

 membranous labyrinth of the two sides. He states that the most 

 characteristic feature of the labyrinth in Clupeoids is the much 

 thickened connective tissue of its walls. Structurally, this tis- 

 sue is "eine fast homogene Grundermasse mit dunkleren fibrosen 

 Streifen und den fiir das Labyrinthgewebe so characterischen 

 Spindelzellen." This dense tissue is well developed on the upper 

 and inner walls of the utriculus from whic*h it goes over to the 

 anterior wall of the sacculus. It is not limited to the wall of the 

 labyrinth, however, but continues off from it quite independ- 

 ently; it extends under the brain, it bridges the space between 

 the two anterior capsules, and becomes continuous with the 

 corresponding tissue of the other side; it also crosses over the 

 cerebellum from one superior sinus of the labyrinth to the other. 

 Hasse had made out enough of these relations to enable him to 

 suggest that this tissue is a condensation of the dura mater. 

 But since Hasse's time Sterzi ('01) has shown that the dura 

 mater is first differentiated in the Amphibia, and that in fishes 

 the covering of the brain consists merely of an undifferentiated 

 meninx primitiva surrounded by a perimeningeal tissue. Ty- 

 sowski thinks that the true explanation of this dense tissue is 

 that it represents a transitional stage in differentiation from the 

 perimeningeal tissue into the envelope of the membranous laby- 

 rinth. The spaces in this tissue he considers as belonging to the 

 membranous labyrinth, and hence properly called perilymphatic 

 spaces. In these spaces are strands of elastic tissue which stain 

 by the Weigert method; they doubtless develop by transforma- 

 tion of connective tissue. If we imagine these spaces developing 

 around the whole labyrinth, we shall have spaces actually 

 homologous with the perilymphatic spaces of higher forms. 



