260 



COMPARATIVE ANATOMY 



CHAP. 



outgrowths of their posterior lamella?. They are divided internally 

 by lamella? into numerous compartments and chambers, in which 

 the developing spermatozoa lie, and are in open communication 

 with the body cavity. The manner in Avhich the sperm formative 

 cells pass out of the testes into the sperm sacs is not known. 

 The sperm sacs, even in nearly related genera and species, differ 

 considerably in their number and special arrangement. In some 

 Lumbricidce a middle unpaired portion is formed, a sperm capsule, and 

 the sperm sacs then appear merely as paired appendages to this 

 capsule. In the Chcetogastridce alone no sperm sacs are developed. 



for bl 



4 



\ \ \ 



b?rL> dfy to 



FIG. 174. Lumbricus agricola. Genital organs, after Vogt and Yung. To the right the 

 sperm sacs and a part of the unpaired sperm capsule are removed. 6m, Ventral chord ; sfj, sU, 

 receptacula seminis ; ?j, U, sperm funnels ; s&, unpaired sperm capsule ; di, dissepiments cut off 

 at their bases ; vd, vas deferens ; fo, funnels of the oviducts ; o, ovaries ; ov, oviduct ; di\, part of 

 the dissepiment between the 13th and 14th segments ; sfy, sb*, sb 3 , paired sperm sacs ; Tij, 7io, 

 testes ; VIII-XV, Sth to 15th segments. 



The sperm formative cells in this family develop fully in the body 

 cavity, and the ripe spermatozoa are collected direct out of the coelomic 

 fluid by the funnels of the sperm ducts. Each sperm duet consists 

 of a preseptal funnel, and of a duct which penetrates the septum 

 and opens externally through a widened terminal division, the 

 atrium (arising by an invagination of the outer integument). Where 

 only one pair of testes is present there is generally only one pair of 

 sperm ducts. This is the case in the Naidomorpha, Chcetogastridce, 

 Tubificidtr, and EncMtrae'ulc. In other Oligochceta, however, especially 

 those which live on land, and in most I/wmbriculidce, there are two pairs 

 of sperm ducts. In this case all the four ducts are either entirely 



