THE ANATOMY. EGG-SACS 97 



extremely conspicuous to the naked eye in spite of their minute size, seems to 

 indicate that they have some function. In the large and important family of the 

 Eudrilidae there appear to be invariably a pair of egg-sacs present ; but in every 

 case the egg-sacs appear without doubt to be functional though they are no larger 

 or but little larger than in Lumbricus ; in this family the passage of ova into the 

 egg-sacs is nearly always facilitated by peritoneal sacs, which enclose the ovaries 

 and form a closed duct leading to the egg-sacs ; I refer again to these in describing 

 the Eudrilidae. In all the Eudrilidae the egg-sacs in mature individuals contain 

 not merely ripe ova, but ova in various stages of development surrounded by 

 masses of ovarian cells ; this state of affairs is similar to what is found in the 

 lower Oligochaeta, where masses of cells are broken off from the ovary and find 

 their way into the egg-sacs, where they undergo further development ; in these 

 cases, therefore, there is a closer likeness as regards function between the egg-sacs 

 and the sperm-sacs, for in both the genital products undergo at least the final 

 stages of development ; whereas in Lumbricus only ripe ova without any attached 

 cells lie in the egg-sacs. 



One pair of egg-sacs have be6n found in the same segment (the fourteenth) in 

 the Acanthodrilidae, the Cryptodrilidae, Geoscolicidae, and certain Perichaetidae ; as 

 a rule egg-sacs seem to be absent from the smaller and degenerate species ; thus 

 they do not appear to exist in Ocnerodrilus or in Gordiodrilus. In many Peri- 

 chaetidae the egg-sacs are interesting from the fact that there are two pairs of 

 them ; I have pointed out that to the two pairs of testes correspond as a rule 

 two pairs of sperm-sacs ; now there does not appear to be any earthworm in which 

 there are normally two pairs of ovaries, though in many there are traces of a second 

 pair, especially in development ^ ; we should expect, therefore, that originally, at any 

 rate, two pairs of egg-sacs existed in correspondence to these two pairs of ovaries. 

 And in the genus Perichaeta (s. s ) there are several examples of species in which 

 there are two pairs of egg-sacs. Bergh (5) has remarked upon the presence of two 

 pairs in a species nearly related to Hoest's Perichaeta hasselti ; one pair occupy the 

 normal position, the other lie in the thirteenth segment just above the ovaries ; 

 this is, it will be observed, precisely the position that the second pair ought to 

 occupy, for the missing ovaries belong to the twelfth segment. I have found two 

 pairs of egg-sacs in other species of Perichaeta similarly placed. In Perichaeta 

 I have noticed that these egg-sacs are often rather larger than in Lumbricus, 

 and that they are of an elongated form perhaps more like the sperm-sacs in 



' See WooDWAED (1, 2) for occasional presence of many ovaries. 







