EAR-SWIMBLADDER RELATION IN CLUPEOIDS 227 



only a few delicate fibers remain in them. These spaces are 

 merely tissue spaces formed by modification of the perimenin- 

 geal or perilabyrinthine tissue, and they are probably not 

 directly homologous with the spaces around the labyrinth in 

 higher forms. 



These canals are in direct connection with tissue spaces in 

 the lateral recess. The tissue of this cavity is composed of a 

 meshwork or reticulum of connective-tissue strands or trabec- 

 ular It contains no fat. The spaces of this meshwork are 

 of varying sizes and communicate freely with each other. One 

 very large space (in diameter nearly half of the whole width of 

 the recess) appeared in all specimens which I sectioned and is 

 probably constant. It lies close to the lateral-line canal. It is 

 bounded by a very definite marginal membrane of modified 

 connective tissue. Numerous small deficiencies in the mem- 

 brane, mostly on the mesial side of the space, allow free com- 

 munication with the spaces in the reticular network. These 

 spaces in turn communicate with the perilabyrinthine spaces 

 mentioned above and, together with them, form a complicated 

 system of intercommunicating canals which have a definite 

 relation with the membranous labyrinth and other structures. 



These perilabyrinthine spaces and canals may be considered 

 in three groups, viz., lateral, subcerebral, and supracerebral. 



The lateral group of spaces consists of the tissue spaces of the 

 lateral recess which have been described above. They are 

 immediately continuous (figs. 11 and 12) with the utricular 

 subcerebral canal under the recessus utriculi. They also com- 

 municate w T ith the supracerebral canal through an opening in the 

 triangular plate (TPP) and the reticular spaces which lie lateral 

 to the utriculus and the superior sinus. 



The subcerebral group comprises two canals, the utricular 

 subcerebral canal and the saccular subcerebral canal. These 

 canals are excavated from the lower surface of the subcerebral 

 perilabyrinthine plate (fig. 11, USC and SSC). The lumen of 

 both is occupied by an exceedingly sparse network of very deli- 

 cate connective-tissue fibers. The utricular subcerebral canal 

 is the more anterior and runs transversely across the floor of 



