WORMS. 



The specimens which arc needed for the lessons 

 upon worms are the common earthworm, and the 

 Nereis.* 



To obtain the most satisfactory results with the earth- 

 worm, living specimens should be placed in a deep 

 soup dish filled with fresh water. Abundant moisture 

 is necessary to these worms ; indeed, they cannot 

 breathe freely unless their skin is dam]), so that this 

 treatment is not as cruel as it seems. The pupils 

 should be led to observe that the body is long, cylindri- 

 cal, and divided into rings or segments. The number 

 of segments cannot be easily ascertained in the living 

 animal, but in prepared or alcoholic specimens from 

 one to two hundred may be counted, the number vary- 

 ing with the size of the worm. The deeper constrictions 

 which form the rings are supplemented, in this creature, 

 by shallower folds, or false constrictions, encircling the 

 body, and dividing the surface of each true ring into 

 two parts. These are mere skin folds, and, therefore, 

 in counting the number of rings, it must be borne in 

 mind that the true rings are only half as numerous as 



* The common name for the Nereis is the "sea-centipede," 

 hut it is misleading, as the structure of the worm is very differ- 

 ent from that of the well known land animal, Centipede, of the 

 class of Myriapoda. 



