734 EDWIN S. GOODRICH. 



nephridia tliemselves, to whicli we may now turn, will afford 

 further evidence in favour of the views advocated above. 



The Nephridium. — It will be readily seen from the facts 

 summarised above that three distinct types of nephridia are 

 found amongst Polych^te worms. 



The first type, found for instance, in Alciope, has no 

 internal opening. The second type, as in Nereis, opens 

 into the coelom by means of a true nephrostome. The third 

 type, as in Polymnia, is a compound organ, formed by fusion 

 with the genital funnel. 



Which of these three types is the most primitive ? Are 

 they to be looked upon as three stages in the development 

 of any one of them, or as three divergent forms derived 

 from some ancestral type ? These are some of the questions 

 which immediately suggest themselves, and it will help us to 

 answer them if we first consider an objection that may be 

 raised against the arguments put forth above with regard to 

 the secondary nature of the connection between the ne- 

 phridium and the genital funueh 



It may, indeed, be said that the facts can be interpreted in 

 exactly the reverse order. 



That, in the Phyllodocidffi, Capitellid^, and Hesionidae, 

 for example, we are not dealing with nephridia which be- 

 come gradually more and more closely connected with the 

 genital funnel ; but, on the contraiy, that the wide-mouthed 

 '^ nephridia" of the Spionid^, Terebellidae, etc., represent 

 the primitive condition of things, and that we can observe in 

 the series described the gradual separation from its duct of 

 the nephridial funnel, and its subsequent acquisition of an 

 opening of its own to the exterior for the extrusion of the 

 genital products.^ 



* Those who support the view that the separate genital funnels in the 

 Polychseta are not primitive organs, might point to Polygordius as an example 

 of a primitive form in which these funnels have not yet become separated off 

 from the nephridium. But such a statement, if accepted, would prove too 

 much. For if Polygordius really occupied the position assigned to it near 

 the base of the Annelid stem, it is surely in this of all worms tiiat we siiould 

 expect to find tlie nephridium opening into the ccelom by means of a wide 



