CHAPTER VI. 



THE WORMS. 



The path which led up to the branch of Ccelenterates 

 passed naturally, so to speak, by way of the 

 group Gastrseads,* and the sponges; 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 Infusorians, though per- 

 haps a Dicyema-like form 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 earih- 

 FiQ. 37.— "Brain" worm, and then place it on the table or desk in a 

 nervoiM^ or gan^ ^^^ '^^^ ^'^^ watch its movements and appearance, 

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

 the earth-worm. ... ^.i, j ^.j^it ^ ^, 



h, brain, or first jomts or segments; these are due to mfoldrngs of the 



pair of ganglJa; muscular skin at regular intervals. Though both 

 ynx; d, oBsopha- enils,of the long, slender, cylindrical body arc much 

 ^oe °o^pi^ alike, the observer will soon be able to distinguish 

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

 «t the 6tif to 8th ^^^^ ^°*''* ^i''^ °f ^^^ body repeat each other, and 

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



to^ftrel seemaS^ side, the worm lying on the latter side. The student 

 a, nerve-flireads ^u now be able to understand the following defl- 

 or commiSBures. . r ., i, ^ e ^ u- x. ^r. 



nition of the branch of worms, to which there are 



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

 * Gastraeads (Dicyema) are without pores, and are simpler than sponges. 



