1911] Watson: The Genus Gyrocotyle. 417 



VIII. SENSE ORGANS. 



The presence of sensory end-organs in cestodes has been 

 several times suggested, but, never established to the satisfaction 

 of investigators in general. Lang (1891) says "The cestodes no 

 longer possess any specific sensory organs." Braun (1894) in 

 Bronn's Thierreich (p. 1300) quotes Blumberg (1877) as observ- 

 ing nerve endings in the limiting membrane or cuticle of the 

 Taenia of horses. These endings are in the form of delicate 

 threads terminating in a swollen knob. Braun thinks that, con- 

 sidering Zernecke 's observations, it seems probable that Blumberg 

 saw actual nervous end-organs. Linton (1891) briefly describes 

 an organ of hearing in Otobothrium crenacolle, as a small struc- 

 ture covered with hairs, situated on the bothridia. Beyond these, 

 and Schiefferdecker 's (1874) interpretation of flame-cells as 

 nerve endings; there are no references to sense-organs in the 

 literature of cestodes, in so far as that is known to the writer. 



In Gyrocotyle the whole acetabulum functions much as does 

 the proboscis of the rhabdocoelan Proboscidea, as a highly 

 efficient organ of exploration, or one might say of touch. While 

 the whole surface of the acetabulum is richly innervated, there 

 are on the margin of the opening of the acetabulum two ridges 

 with a peculiar and significantly rich nerve supply, and two shal- 

 low pits in which lie flat plates of nervous tissue, end-organs of a 

 pair of heavy branches from the anterior lateral stem above 

 referred to. 



1. The Sensory Ridges or Papillae. These lie one on each 

 side of the latero-dorsal margin of the acetabular opening. A 

 nerve from the anterior lateral stem spreads out within each 

 "papilla," its branches running to the base of the very thin 

 limiting membrane. 



2. The Sensory Pits (sens, pits, pi. 36, figs. 23, 25) lie 

 farther laterad than the papillae, and on the opposite or ventral 

 surface of the acetabular margin. They consist of a definite 

 depression, covered with a differentiated membrane, immediately 

 beneath which lies a plate of nervous tissue, formed by a very 

 heavy branch from the anterior longitudinal nerve. This does 

 not break up but ends abruptly as a plate of nervous tissue 



