in some Chcetopod Annelida. 325 



The second species, Nais rivulosa, already described by Leidy 

 (Journal Acad. Nat. Sc. Philad. 1850, vol. ii. pt. 1. p. 43) very 

 closely resembles the European Nais elinguis, w4th which D'Ude- 

 kem regards it as identical. The third species, Dero limosa, has 

 also been described by Leidy (Proc. Acad. Philad. 1857, vol, v. 

 p. 226), and, though overlooked by D^Udekem, appears to be 

 distinct from the European form of the same genus. The fourth, 

 EnchytrcEus triventralopectinatus, I have not been able to identify 

 with any species described in works at my command, and have 

 therefore named from the three anterior pairs of ventral combs 

 after which the dorsal combs begin. This character appears to 

 distinguish it from E. socialis, if I may judge from the figure 

 given by Leidy (Journ. Acad. Philad.). It has no eyes. The 

 pharynx extends nearly to the fourth ventral or the first dorsal 

 combs, from which a narrow oesophagus continues to a little 

 back of the sixth ventral combs. Here a gradual enlargement 

 of the alimentary canal occurs, ending abruptly just back of the 

 eighth, in a naiTow twisted tube ; and this last gradually enlarges, 

 at the ninth ventral combs, into a modei*ate-sized alimentary 

 canal, in which I observed nothing specially marked. The entire 

 length of this Naid was about f inch. 



The occurrence of spontaneous fission in Stylaria {Nais) pro- 

 boscidea is described as follows by Miiller : — " If a virgin Naid, 

 as I may call it, with 16 or more pairs of hair combs, or 20 or 

 more pairs of hook combs [there are 4 pairs of hook combs 

 anterior to the first hair or dorsal combs as in Nais and Dero], 

 be carefully observed, it will be seen that its anal ring slowly 

 elongates, and, after some days, appears to be transversely marked 

 within into rudiments of future rings*. In each of these divi- 



Lamarck et Ehrenberg, parce que cette espSce ne differe des autres Nais 

 que par Tallongement tres grand de la levre superieure. Ce caractere 

 n'etant accompagne d'aucune modification importante dans la forme des 

 autres organes, je ne puis le eonsiderer comme assez tranche pour servir a 

 former un genre nouveau." There is, however, a marked difference in the 

 form and position of the cordiform anterior enlargement of the alimentary 

 canal, which even the statements and figures of Miiller and Gruithuisen 

 indicate, between the Naids wich a long upper lip or proboscis and those 

 with a short one; and the manner of fission differs in these two groups, as 

 will be shown. Lamarck's genus Stylaria is therefore a good one. Ehren- 

 berg's division of this genus, however, based upon the absence of eyes, is 

 unfoimded ; for I have seen Nais rivulosa lose them without any other 

 apparent change, and Agassiz has stated that this occurs as a part of the 

 normal development in many Naids. 



* Schultze considers Miiller in error as to the position at which fission 

 t xkes place, because he describes it as occurring in a segment, and not 

 between two. The difference of statement, however, is simply verbal, as 

 Miiller speaks of " die Zwischenraume der Borsten oder die Gelenke," 

 p. 26, and in many other places shows very plainly that such is his meaning. 



