﻿V.] THE FRESH-WATER MUSSEL. 329 



lobe of an animal which has been killed under 

 chloroform. Conspicuous among the cells thus 

 isolated there will be found large oval or rounded 

 ones, each lodging a central refractive globule. 



b. Remove the mantle-lobe from a mussel which has 

 been killed as above and subsequently preserved 

 in alcohol, and split it into two. Transfer a 

 portion of one half to a glass slide, torn surface 

 upwards, and treat with iodine solution; the 

 whole will be studded with small brown spots. 

 Examine under a high power ; the spots are seen 

 to be identical with the globules observed in 

 a. (their chemical reactions are those of gly- 

 cogen). 



I. The nervous system. 



i. Pin the animal down so as to get the body absolutely 

 rigid ; remove the mantle-lobe and gills of one side 

 and slit open the organ of Bojanus. 



Wash until quite clean and examine under water. 



a. Find the cerebro-splanchnic commissures; two parallel 

 white cords traversing the excretory organ. Trace 

 the near one backwards; it passes round the 

 posterior retractor tendon towards the under side 

 of the posterior adductor muscle. Turn this latter 

 over, so as the better to display its under surface, 

 and note 



l>. the parieto-splanchnic ganglia; two elongated yellow 

 masses confluent in the middle line, seen on 

 removing the membranous investment from the 

 ventral surface of the above-named muscle. They 

 distribute branches to the same, to the gills and 

 pallial lobe. 



