Turner, Nervous System of Cypris. 41 



considers this a rudimentary organ. Its morphology varies in 

 different species. By Dr. Wenzel Vavra the variations that we 

 meet with in this organ are considered to be of taxonomic value. 

 On the tip of the third and fourth segments of the mandi- 

 bular palp of certain Cypridcs, there occurs a short dagger- 

 shaped setose seta [fig. 23 D.S.\ This seta was first described 

 in the " Entomostraca of Minnesota." ^ This seta occurs in : 

 Candona croginani Turner, Candona delazvarensis Turner, Cypri- 

 dopsis vidua O. F. Miiller, Cypris herricki Turner, Cypri?iotus 

 burlitigionensis Turner. 



Recapitulation. 



I. The nervous system of Cypris consists of a supra- 

 oesophageal ganglion, which is connected to a ventral chain by 

 a pharyngeal collar. 



2. The ventral chain consists of an infra-oesophageal and 

 two subsequent ganglia. The infra-oesophageal ganglion has 

 probably been compounded out of at least three pairs of ganglia. 



3. From the supra-oesophageal ganglion arise one un- 

 paired and two paired nerves. These nerves are : the optic, 

 the antennulary, the antennary. The antennary nerve receives 

 a portion of its fibres from a ganglion that lies within the phar- 

 yngeal collar. The nerve itself arises from the point where 

 the collar joins the supra-oesophageal ganglion. 



4. From the infra-oesophageal ganglion arise five pairs of 

 nerves. Four of these pairs arise from the ventral portion of 

 the ganglion, while the other arises from the dorsal. The four 

 that arise from the ventral half are : the labial, the mandibular, 

 the labral, and the first maxillary. The one that arises from the 

 dorsal portion is the thoracic nerve. 



5. The labial nerve passes forward into the pharyngeal 

 collar before leaving the central nerve chain. 



6. The thoracic nerve innervates the shell muscles. 



^ C. L. Herrick and C. H. Turner. Synopsis of the Entomostraca of 

 Minnesota with descriptions of related species comprising all known forms from 

 the United States included in the orders Copepoda, Cladocera, Ostracoda. St. 

 Paul, Minn., 1895. 



