354 PHYSIOLOGY OF THE INVERTEBRATA. 



sight, hearing, and smell. Its sensitiveness to touch and its 

 dislike to sunlight are well known ; and, though not possessed 

 of organs of sight or smell, it is able easily to find its way to 

 stores of food, and to retreat from sources of danger into a 

 burrow " (Gibson), 



In Alciojje (one of the PolycJmta) the eyes are large and 

 well developed. 



As already stated the visual organs in the Annelida are 

 usually situated in the anterior part of the body ; but in " the 

 remarkable genus Polyophthcdnius, De Quatrefages discovered, 

 besides the ordinary cephalic eyes, a double series of 

 additional visual organs, one pair being allotted to each 

 somite. In Branchiomma, eyes are situated at the ends of 

 the branchial plumes, Ehrenberg has described two caudal 

 eyes in Ampldcora, and De Quatrefages has shown that 

 similarly placed eyes exist in three other species of Polychaia , 

 two of which are closely allied to Amj^Mcoi^a, while the other 

 is an errant form, related to Lumhrincrcis. Auditory sacs, 

 containing many otoliths, have been observed upon each 

 side of the oesophageal ring in Arcnicola, and similar organs 

 have been noticed in other Tuhicola ; but hitherto their 

 existence has not been certainly determined in the Errantia " 

 (Huxley). 



The Nematoscolices. 



In the Nematoidca, the papilla and hairs situated chiefly in 

 the region of the mouth are organs of touch. 



In non-parasitic Nematodes {c.//., Enojjlus) pigmented 

 ocular spots are present on the cesophageal nervous ring. 



The Ch^tognatha. 



The eyes in Sagitta are situated on the supra-cesophageal 

 or cerebral ganglion. 



