86 OLIGOCHAETA 



they furthermore agree so closely with the testes that in the early stages it is 

 impossible to distinguish the two kinds of gonads save only by the segment which 

 they happen to occupy. Not only is there this close agreement in structure (in the 

 immature condition) and in situation, but the shape of both gonads is at first 

 identical ; the immature ovary like the immature testis is somewhat pear-shaped in 

 outline, the broader end being attached to the septum ; later on the free end of the 

 ovary, as is also the case with the testis, may become frayed out into a number of 

 processes. The ovaries always lie behind the testes ; the only possible exception is 

 in the genus Plutellus, where PEKRTER (8) has stated that the ovaries are in front 

 of the testes; if, however, a worm described by BENHAM (8) as a Plutellus is really 

 a member of this genus, there is nothing abnormal in the position of the female 

 gonads. As a rule the gonads are all in consecutive segments, the ovaries following 

 the testes, the rule indeed has very possibly no exception ; this at first sight appears 

 to be an inaccurate statement ; for in Lumbricus, and indeed in all earthworms, the 

 ovaries are in the thirteenth segment, while the last pair of testes, if there are two pairs, 

 is in the eleventh segment ; there is thus a gap of a segment between the last testis and 

 the ovary of its side of the body. In embryos of Lumbricus, however, as was shown 

 by WOODWARD, and in embryos of Octochaetus, as has been demonstrated by myself 

 (51), there is an additional pair of ovaries in the twelfth segment, which never comes 

 to maturity and disappears early. There are, therefore, some grounds for believing 

 that two is the typical number of pairs of these gonads in the Lumbricidae and 

 AcanthodriKdae, and very likely in other terrestrial forms also. The fact that there 

 are two pairs of testes seems to render this assumption probable at least. In the 

 genus Phreoryctes the number of ovaries (as of testes) is normally two pairs. 

 Another fact pointing to the same conclusion is the presence in more than one 

 species of Perichaeta of two pairs of egg-sacs ; there is a pair in the fourteenth 

 segment and another in many cases in the thirteenth segment ; the latter would appear 

 to correspond to a missing pair of ovaries belonging to the twelfth segment. 



In fact both lines of argument appear to point to the primitive possession of two 

 pairs of ovaries at any rate in the terrestrial Oligochaeta. The passage of ova from 

 the gonad into the duct and still more into the egg-sac in the terrestrial Oligochaeta 

 is not easy to understand ; as to the former it must be remembered that in the living 

 worm the distance is not great between the gonad and the large mouth of the 

 funnel; it is possible that from time to time during the movements of the worm the 

 distance is lessened ; when this takes place the oviducal funnel may approach so near 

 to the gonad that the movement of its cilia may perhaps detach a perfectly ripe 

 ovum from the extremity of the ovary and direct its course into the funnel, and 



