92 OLIGOCHAETA 



because that term suggests a comparison with the similarly named structures of 

 vertebrates, which are a part of the efferent apparatus ; at first the structures now 

 known to perform the function of harbouring the sperm were regarded as testes ; in 

 spite of the discovery by HERING of the real testes, the sperm-sacs were persistently 

 termed the testes by almost everybody. From the fact that the sperm-sacs always 

 appear to contain Gregarines, these organs were once regarded as ovaries the 

 Gregarines when encysted being mistaken for the ova ; D'UDEKEM'S discovery of the 

 ovaries disposed of this view as well as of the alternative view due to VON SIEBOLD 

 that the sperm-sacs were hermaphrodite glands. 



Their true nature was first pointed out by HERING who called them ' Samen- 

 blasen.' The development (in Lunibricus) was first elucidated by BERGH, whose 

 discoveries finally disposed of the theory that the organs were testes. The sperm- 

 sacs originate from the intersegmental septa, as outgrowths of the same ; they 

 contain from the first a cavity which is continuous with the cavity of the segment 

 from the wall of which they arise ; this cavity is therefore coelomic ; later on it is 

 divided up into a series of inter- communicating spaces by the complicated growth 

 of the walls ; but none the less the internal cavity remains coelomic, and the 

 epithelium found within it is peritoneum. The sperm-sacs are in fact coelomic sacs 

 set apart for the maturation of the sperm. It is usual to distinguish between the 

 paired sacs and median unpaired sacs which enclose, when present, the gonads, the 

 ventral blood-vessel and even the nerve-cord, besides of course the funnels of the 

 sperm-ducts. These communicate in the adult with the paired sacs ; the name 

 sperm-reservoirs may be applied to the former, that of sperm-sacs may be reserved 

 for the latter. As to the origin of the sperm-reservoirs there does not appear 

 to be much positive information ; BLOOM FIELD thinks that they are due to a 

 coalescence between the paired sacs ; BERGH is not apparently inclined to back up 

 this view. It can hardly be doubted that they originate from the septa as do the 

 paired sacs ; they differ, however, in structure to a certain extent ; the cavity of the 

 paired sacs, as has already been stated, is subdivided into numerous cavities ; that 

 of the median sacs is not so divided ; the median sacs are by no means always 

 present ; they are absent, for example, in the genus AllolobopJiora ; they seem also 

 to be absent in Acanthodnlus and in a number of other forms. In these genera it 

 of course follows that the gonads and the sperm-duct funnels hang freely into the 

 cavity of their respective segments. It is not always possible to refer a given 

 structure to one of these two series of sacs ; the matter becomes easier if we agree 

 to apply the term sperm-reservoirs to those sacs which enclose the gonads and the 

 funnels, reserving the term sperm-sacs for diverticula of the septum which do not 



