EAR-SWIMBLADDER RELATION IN CLUPEOIDS 221 



accurate morphological value. The term 'perimeningeaF 

 must be retained for the undifferentiated tissue around the 

 brain and labyrinth, and cannot, therefore, with defmiteness be 

 applied to structures differentiated from it. The term 'peri- 

 lymph' or 'perilymphatic' which has been used by previous 

 writers in this connection is subject to the same objections which 

 Streeter ('17) has advanced in discussing the somewhat analo- 

 gous structures around the membranous labyrinth in higher 

 vertebrates. 



The term 'periotic/ or 'perioticular,' as it has been applied to 

 the tissues and spaces around the membranous labyrinth of 

 higher vertebrates is also objectionable in the case of the Clupe- 

 oids. Only a small part of the labyrinth in these fishes is en- 

 closed in an auditory capsule. The tissues and spaces around 

 the labyrinth are, therefore, continuous with, and never dif- 

 ferentiated from, the corresponding structures around the 

 brain, but they form a part of an extensive system of differen- 

 tiated tissues and spaces which extend through the perimenin- 

 geal tissue both above and below the brain and which reach out 

 through the lateral recess of the skull to the lateral-line canals. 

 These relations are obviously different in many respects from 

 those of the spaces around the membranous labyrinth of higher 

 forms to which Streeter applied the term 'periotic' or 'perioticu- 

 lar.' The use of this term in the case of the Clupeoids implies 

 an homology which is certainly not complete and which prob- 

 ably has little, if any, morphological significance. 



The term 'perilabyrinthine' has therefore been chosen to 

 apply to all the specialized, condensed tissue and the spaces in 

 it, which are developed around the membranous labyrinth and 

 their extensions over and under the brain. 'PerimeningeaP 

 will be used as is customary (following Sterzi) to designate all 

 the undifferentiated tissue between the meninx primitiva and the 

 cranial wall. It may be noted here that in certain regions of the 

 Clupeoid skull this tissue extends through large apertures in the 

 cranium and becomes continuous with the subcutaneous tissue, 

 particularly in the neighborhood of certain parts of the lateral- 

 line canals. Here accurate use of terms may be sometimes dim- 



