DESCRIPTIONS OF GENERA AND SPECIES 305 



I follow Lankester (note appended to Bourne's paper 5) in relegating the genus 

 Chaetogaster to the family Naidomorpha ; so long as the genus Chaetogaster alone 

 was known, the entire absence of the dorsal seta-bundles might possibly be held 

 to be of sufficient importance to keep it as the type of a distinct family, though 

 doubtfully, in view of analogous differences in the family Enchytraeidae ; now, however, 

 that another genus, closely allied to Chaetogaster, viz. Amphichaeta, is known, there 

 is not this excuse for retaining the family; no other structural differences of first- 

 rate importance support such a separation of the Chaetogastridae as a distinct 

 family. The absence of the ventral setae in a number of the anterior segments 

 (not from the first) was a peculiarity which might possibly merit emphasis of this 

 kind, were it not for an analogous absence from two segments of the ventral setae 

 in Ripistes Tnacrochaeta. The reproductive organs, whose modifications are frequently 

 of family value, are constructed upon precisely the same lines as in other Naidomorpha ; 

 and the spermathecae, testes, &c., are in the same segments in both of the ' families ' 

 Naidomorpha and Chaetogastridae. I have mentioned as a characteristic of the 

 genus the fact that there is only a single pair of commissural vessels uniting the 

 dorsal and ventral vessels ; this is not absolutely distinctive, since Bourne found, 

 and I have been able to confirm his discovery, that in Pristina equiseta there 

 is but a single pair of such vessels. A marked characteristic of the present genus 

 is the series of dilatations of the oesophagus ; in Ch. crystallinus, for example, there 

 are two of the dilatations following the pharynx ; each is covered with a network 

 of blood-vessels ; they, no doubt, correspond to the ' magen-ahnliche ' dilatation in 

 many Naids. But they are absent in Ch. filiforonis, which is very Naid-like. 



The absence of an intimate correspondence between the nerve ganglia, the inter- 

 segmental septa, and the setae is remarkable. The first septum occurs behind the 

 pharynx and there are three ganglia in front of it, to which there are only one 

 pair of setae bundles. 



The remai'kable double character of the ventral nerve cord in the anterior segments 

 has already been commented upon. 



The nephridia of the genus, like those of Amphichaeta, are without a funnel ; the 

 place of this is taken by a rosette-shaped bunch of cells attached to the anterior 

 septum of the segment by a few muscle fibres. The development of the nephridium 

 has been traced by Vejdovsky, who found no trace of a funnel at any time ; the 

 earliest stage which he figures consists of three cells, all of them lying behind the septum. 

 The mature organ consists of tubes running parallel to each other for the greater 

 part of their course ; they are connected by numerous small tubules, which also branch 

 within the secreting cells. 



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