THE ANATOMY. REPRODUCTIVE SYSTEM 



93 



Fig. 26. 



enclose these organs. Looking at the matter in this way, the sacs in Moniligaster 

 must be regarded as sperm-reservoirs, although they are paired; the sacs in question 

 enclose the gonads and the funnels, and it will also be noticed that their cavity is 

 undivided by trabeculae — another feature which characterizes the sperm-reservoirs 

 of Lumbricus in contradistinction to the sperm-sacs. It appears from the results 

 obtained by Bergh and Vejdovsky that the paired sperm-sacs are 

 developed before the median sacs ; hence it would seem just to 

 regard these sacs as older than the median sacs. It is conceivable 

 that the median sperm-reservoirs of earthworms are more strictly 

 comparable to the generally impaired and very voluminous sacs 

 found in the aquatic Oligochaeta, than are the sperm-sacs. 



In only one family of Oligochaeta are the sperm-sacs nearly 

 always absent^ this family is the Enchytraeidae ; the genus Mesen- 

 chytraeus, however, has paired sperm-sacs, which originate from 

 the septum bounding posteriorly the segment in which the male 

 gonads lie. The number and arrangement of the sacs varies 

 considerably in different genera, thus affording valuable characters 

 which are sometimes of specific value only. The number of the 

 sperm-sacs varies from one to four pairs. The aquatic forms have 

 only a single pair or a single sac which usually extend through 

 a large number of segments, enclosing the egg-sacs in many cases, 

 as in Rhynchelmis figured by Vejdovsky (9). In the terrestrial 

 worms the sperm- sacs are as a rule of comparatively small size; 

 they rarely occupy more than a single segment. There are various 

 exceptions to this rule, however; and these exceptions always 

 concern species or genera in which the number of the sperm- 

 sacs is reduced to one pair. The most remarkable instances are 

 Polytoreiitus (Woodcut, fig. 36) and Trichochaeta ; in both of these 

 genera there is one pair of sperm-sacs which extend backwards 

 through twenty or thirty segments ; the extent of these sacs is 

 only paralleled by certain aquatic genera such as Rhynchelmis. It 

 is time that when the sperm-sacs are of such an extraordinary length they are thin ; 

 but in spite of this the total space enclosed by them is greater than in the case of 

 the genera where there are two or three pairs of sperm-sacs only, occupying a single 

 segment each ; unfortunately our knowledge of the economy of these worms does not 

 at present permit of any explanation of these remarkable divergences. 



Neuland has recently recurred to the earlier view respecting the sperm-sacs ; he considers 



POLYTOEEUTUS. 



EEPEODUCTIVE 



ORGANS. 



I. Anterior end of 

 sperm-sacs. 2. Dilated 

 region of sperm-duct. 



3. Calciferous gland. 



4. Oviduct. 5. Spermi- 

 ducal gland. 6. Sper- 

 mathecal sac. 7. Pos- 

 terior end of sperm-sac. 



