36 Journal of Comparative Neurology. 



from the side, this is a pear-shaped organ, with its base directed 

 outwards (ectad) and its apex inwards (entad). 



In ha^matoxyhn preparations, in the base of this pear- 

 shaped organ, there is a densely stained circular disc. In Cy- 

 prinotiis incongritens {Kamdohr) this disc is 12.92 micromillime- 

 ters in diameter [fig. 34]. 



The apex of this organ is surrounded by a ganglion of 

 nerve cells [fig. 34]. 



The length of this organ varies in different species. In a 

 general way, the larger the species the larger this sense organ. 

 In Cyprinotiis incongruens Ramdohr, which is about 1.35 milli- 

 meters in length, this organ is 35.53 micromillimeters long and 

 32.3 micromillimeters wide; while in Cypris Jierricki Turner, 

 which is about three millimeters in length, this organ is 71.06 

 micromillimeters long and 48.45 micromillimeters wide. In 

 other words, in Cypris Jierricki, which is about twice as long as 

 Cyprinotus incongruens, the pear-shaped sense organ is about 

 twice as long as the corresponding organ of Cyprinotus in- 

 conguens. 



This organ is situated a short distance below the base of 

 the antenna and close to the outer wall of the body. The broad 

 base Hes in contact with the body wall [fig. 16, P\. 



Since this organ is much larger in Cypris herricki Turner 

 than in any other form known to me, the following histological 

 study of the organ is based upon sections of that species. 



From a histological standpoint, this pear-shaped organ is 

 composed of a neuroglia-like matrix, in which are two transverse 

 rows of nuclei. One of these rows of large nuclei is located 

 about half way between the base and the apex, while the other 

 row is situated near the apex. Near the base of this organ the 

 matrix is denser than it is elsewhere [fig. 31]. The organ is 

 surrounded by a nucleated epithelium. 



This organ is innervated by a branch of the labial nerve 

 [fig. 16]. 



There is a pair of these organs, but they are so closely ap- 

 proximated that a hasty glance might not reveal both members 

 of the pair. 



