PHYLUM ANNELIDA 207 



new. " There is a limit, however, to the ability of fragments 

 to grow into complete worms. If a piece containing only a 

 few metameres is cut from the anterior or posterior end, a 

 double-headed or double-tailed monster, which is incapable 

 of sustaining itself, is produced. Professor T. H. Morgan 

 has made many curious monstrosities by grafting parts of 

 earthworms together individuals with the body single in 

 front and double behind, long composite worms made by 

 fusing parts of two or three individuals, etc. 



Earthworms escape dry seasons and the cold of winter by 

 burrowing deep in the ground and collecting together in 

 clumps for mutual protection. The slime which is secreted 

 from the surface of the body forms a tough coating on the 

 inside of the burrow so that there is little -danger of ob- 

 struction by the caving in of dirt. The tunnel is thus 

 always open for a quick retreat if the necessity arises. 



Race Preservation. Earthworms are hemaphroditic but 

 not self-fertilizing. During the breeding season two in 

 dividuals frequently come together so that their anterio 

 ends overlap, and a slime tube is secreted about th 

 bodies of both (Fig. 83, B). The openings which discharge 

 spermatozoa in each worm are thus brought opposite the 

 little cavities for receiving sperm in the other individual. 

 When the pair separate each has been supplied with sperm 

 by the other (that is, four little pockets in the skin have 

 been filled with spermatozoa), and each is prepared to lay 

 fertile eggs. 



Every mature earthworm has a smooth swollen region, 

 the clitellum, near the anterior end of the body. This gives 

 off a glandular secretion which forms cocoons for receiving 

 eggs and protecting them during development. When a 

 worm is about to deposit a cocoon the clitellum forms an 

 elastic, membranous band which is slipped off over the an- 

 terior end of the body, just as a ring slips from a finger. 

 As the band passes over the openings of the female repro- 

 ductive ducts, eggs are discharged inside it; and as it goes 

 across the pockets where the spermatozoa are stored some 



