CHAPTER VII. 

 THE WORMS. 



THE path which led up to the branch of Echinoderms 

 passed naturally, so to speak, by way of the 

 sponges, polyps, and jelly-fishes; we must 

 now retrace our steps and take a new path, 

 which will lead us to the worms. This path 

 has not been very clearly pointed out by our 

 studies of nature, but certain of the young 

 of the lowest worms are so simple that it is 

 difficult to tell them from some of the larger 

 Infusoria. Hence the entrance to the path 

 leading to the simplest worms seems pointed 

 out by the higher Infnsorians, though per- 

 haps a hydra-like polyp may be the signpost 

 to the .vermian track. But we first should 

 understand the structure of a true or typical 

 worm. 



" In order to obtain an idea of worms in general, the 

 student may dig up in the garden a common earth- 

 worm, and then place it on the table or desk in a 

 s _ flat dish and watch its movements and appearance, 

 glionated cord of The body will be seen to be formed of numerous 



FIG. 52. "Brain 1 



/i,br C aiii orflrst joints or segments; these are due to infoklings of the 



pair of 'ganglia; muscular skin at regular intervals. Though both 



</. nerves to phar- .. , . . , , 



ynx; d, cesopha- ends of the long, slender, cylindrical body are much 



geal collar; / alike, the observer will soon be able to distinguish 

 by the pharynx; the head -end from the tail-end; he will also notice 



ol 8 th t e h 5th g 'to| I th that both sities of tbe bod y re P eat eacb other, and 

 segments respec- that there is an upper (dorsal) and lower (ventral) 

 tS& seg^nl* side, the worm lying on the latter side. The student 



a, nerve-threads w ju now b e a ^] e to understand the following defi- 

 or commissures. . . . , . , ,, 



nition of the branch of worms, to which there are 



some exceptions, which need not, however, be here mentioned. A 



