356 ESSENTIALS OF ZOOLOGY 



other animal receives a ferment from the salwary glands of the 

 pharynx, which prevents it from coagulating. It is then stored in 

 the diverticulae of the crop. The animal is capable of ingesting three 

 times its own weight in blood, and, since several months may elapse 

 before it is all digested, frequent feedings are not necessary. The 

 coelom is very much reduced due to the excessive development of the 

 mesodermal tissue. Each animal is hermaphroditic. Sperms are 

 placed on the skin of another leech, and they apparently work through 

 it into the ovaries, where fertilization occurs. Development takes 

 place in a cocoon produced by the clitellu7n. Two nephridia are pres- 

 ent. The nervous system is typical of the annelids. 



Class Gephyrea (je fi re' a, bridge). — This class is a group of 

 marine annelids which are nonsegmented, have no appendages, and 

 possess a trochophore larva. They are usually comparatively large 

 and live in shells, crevices, and such other places as will afPord pro- 

 tection. In this class, the representatives of order Echiuroidea have 

 a well-developed prostomium, used in capturing prey and in loco- 

 motion. In Bonellia, the female is the normal individual, while the 

 male has no proboscis, is ciliated, and lives as a parasite on the pro- 

 boscis of the female. Representatives of the order Sipunculoidea have 

 no prostomium in the adult. 



Importance of Annelids to Man and Other Animals 



Even though no casual observer would consider that annelids 

 have any important relationship to other living organisms, they 

 have been found to be of great importance in a number of ways. 

 Darwin concluded from some forty years of observation that the 

 earthworms in an acre of ground could bring to the surface in one 

 year as many as eighteen tons of feces, known as castings. This in- 

 dicates without doubt that these animals are of great value, because 

 in stirring the soil they cover up objects, causing them to decay. 

 Their continuous burrowing through the soil also makes it porous, 

 a necessary condition for plant growth. 



Earthworms have also less desirable qualities. They serve as 

 secondary hosts for parasites of several animals. Most of the para- 

 sites having the earthworm as a secondary host live as adults in 

 birds, pigs, and other animals which use the worms as food. 



They have created a serious problem in some of the. irrigation 

 districts of the Southwest by burrowing through levees until they 



