THE SPERMATOPHORE IN ARENICOLA 1005 
like degenerating spermatogonia. As these worms were selected 
at intervals throughout the year so they would be representative, 
. we may safely conclude that the vessels of nephridia one and six 
never bear active gonads, while there is slight evidence that the 
gonadial vessel of the sixth nephridium bears a degenerating 
gonad. 
The limits of the gonads have not been as carefully studied in 
the other species of the Arenicolidae is in A. cristata. Yet I 
have exmained, macroscopically, several dozen specimens of each 
of the other species, claparedii, ecaudata, grubii and marina and 
have examined microscopically the blood vessels when any doubt 
could exist, with results confirmatory of the statements of pre- 
vious authors, notably Gamble and Ashworth, as follows: A. 
ecaudata has thirteen pairs of nephridia in setigerous segments 
5-17, A. marina six, in segments 4-9, A. grubii and A. claparedii 
each five pairs in segments 5-9. 
Presumably the Arenicolidae have evolved from a more gener- 
alized polychaete in which nephridia and gonads were segmentally 
repeated organs. Both organs have gradually been confined to 
a smaller and smaller region. This gradual reduction seems to be 
well illustrated within the group as indicated by the number and 
position of the nephridia given above. Moreover,according to 
Gamble and Ashworth, the first pair of nephridia of A. marina 
are frequently absent and the last pair occasionally. Lille 
remarks of the nephridia of A. cristata that ‘‘The two earliest 
formed pronephridia, those of somites rv and v, degenerate at a 
comparatively early period in the development. The remaining 
sIx pairs (in somites vi-x1, inclusive) are directly transformed 
into the definitive adult nephridia.”” Fauvel (99) states that 
the number of nephridia in A. ecaudata is only occasionally thir- 
teen; that twelve is the usual number, the last pair of nephridia 
being absent from his specimens. In the two hundred and more 
specimens of A. cristata examined I have found only three cases 
of variation in the number of nephridia. In two of these the 
first pair of nephridia was wanting; in the third only the funnel 
was present in the sixth right. JI have yet to find variation in 
the other species. 
