296 SYNOPTIC COLLECTION. 



tains a sac called a proboscis (fig. 2) which can be turned 

 outward as seen in the figure. It is armed with many 

 fine horny teeth and two stout hooked teeth already seen 

 in the larva. 



Along each side of the body there is a row of fleshy, 

 un jointed, and two-lobed organs, the parapodia (figs, i, 3, 

 4) which are continuations of the body wall (fig. 4). 

 They serve as efficient paddles in locomotion, and the 

 lobes are also differentiated into breathing organs. In 

 the living worm these lobes are bright red in color, owing 

 to the blood contained in them. Extending beyond the 

 edge of the paddles are horny setae (fig. 3) which in real- 

 ity originate within the body cavity and pass outward pierc- 

 ing the body wall (fig. 4). The division of the body cav- 

 ity into segments, which is one of the chief characteristics 

 of worms, is well shown in fig. 3, representing the forward 

 end of Nereis with the proboscis in place. The dorsal 

 part of the body wall has been removed so that six mus- 

 cular partitions are exposed, dividing the cavity trans- 

 versely into as many compartments. There is, moreover, 

 a marked tendency towards the repetition of the paired 

 organs in each compartment, such as the nephridia, the 

 bundles of muscles, and the ganglia of the nervous system. 



The relative position of the three important systems of 

 organs in this class of animals is shown in PI. 736, fig. 4. 

 The digestive system represented by the large central 

 circle takes up the greater part of the body. Immediately 

 above and below it are the long tubes of the circulatory 

 system, cut across in fig. 4. Below the ventral blood 

 vessel is the nerve cord which runs the whole length of 

 the body. 



Autolytus cornutus Ag., (PI. 737. figs. 1-13), is 

 especially interesting as it is one of the few worms that 

 illustrates alternation of generations. The eggs pass from 

 the body cavity of the mother into a bag or pouch which 

 has grown out from the lower side of her body. Here 

 they remain and are brooded over by the parent until the 



