144 ZOOLOG Y 



pharynx is devoid of arTnature. They are hermaphrodite, 



and their reproductive organs are confined to a few segments. 



Their ^ova are laid in cocoons. Their developement is direct. 



The Oligochaeta were at one time divided into two 

 groups : the Terricolae, which live chiefly on land, and the 

 Limicolae, which are mostly aquatic. Eecent research has, 

 however, broken down the structural barriers which were 

 believed to exist between the members of these two groups. 

 The oligochaet worms are now arranged by Benham in a 

 number of families, which allow themselves to be grouped in 

 two divisions : (i.) the Naidomorpha, in which asexual repro^ 

 duction takes place ; and (ii.) the Lumbricomorpha, in which it 

 does not. The earthworm is the most familiar example of the 

 latter subdivision. 



One of the most curious features found in many of the 

 Oligochaets is the dorsal pore. In Zumbricus this pierces the 

 skin on each segment in the middle dorsal line, and places the 

 coelom directly in communication with the exterior. The pores 

 occur in this genus on all the segments except the first six or 

 seven. They are closed by a sphincter muscle, and opened by 

 an anterior and posterior longitudinal band of muscles. They 

 are found in several species of the Oligochaets, — Zumbricus, etc., 

 — but do not occur in Polychaets. Megascolides, a gigantic 

 Australian worm, measuring from 4 to 6 feet in length, ejects 

 through its dorsal pores the milky coelomic fluid with which 

 it coats the walls of its burrows. 



The function of the modified skin of certain segments 

 which constitutes the clitellum is to form the cocoons in 

 which the eggs are deposited. It may completely enclose the 

 body, and is then known as a cingulum, or it may be incom- 

 plete. In the aquatic forms it only includes one segment : 

 that on which the vas deferens opens. The capsulogenous 

 glands also found in the skin give rise to the albuminous fluid 

 found in the cocoon in which the ova and spermatozoa are 

 deposited. This secretion serves to nourish the developing 

 embryos. 



The septa which divide the body internally into segments 

 are almost absent in Aeolosoma ; only one, dividing the head 

 from the body, is present. 



