BRANCH VERMES: THE WORMS 133 



another worm, and finally slips off the head end of the 

 animal. The entire structure with the contained eggs 

 and sperm-cells as it passes off from the body becomes 

 closed at both ends, thus forming a horny capsule which 

 lies in the earth until the young worms emerge. Only a 

 part of the eggs develop in each capsule, the rest being 

 used as food for the growing young. The young earth- 

 worms, though of very small size, are fully formed before 

 they leave the egg-capsule. Earthworms are more or less 

 gregarious, large numbers often being found together. 



For an interesting account of the habits of earthworms 

 see Darwin's- " The Formation of Vegetable Mold." 



OTHER WORMS. 



The branch Vermes comprises so large a number of 

 kinds of animals presenting such great differences in struc- 

 ture and habit that it is impossible to give a brief state- 

 ment in general or summary terms of their external 

 body-characters, of the structural and functional condition 

 of their various organs and systems of organs, and of the 

 course of their development and life-history as has been 

 done for the preceding branches. Many zoologists, 

 indeed, do not include all the worms or worm-like animals 

 in one branch, but consider them to form several distinct 

 branches. 



In certain very general characters all of the animals 



which compose the branch Vermes do agree. All, or 



/ nearly all, have an elongate body which is bilaterally 



\ symmetrical, that is, which could be cut by a median 



longitudinal cutting in two similar halves. In most of 



J them also the body is composed of a number of successive 



\ segments or somites which are more or less alike. This 



kind of segmented or articulated body is also possessed by 



