180 Dr. E. GreefF on Autolytus prolifer. 



fission and gemmation^ only that in Nais these occur very 

 regularly and distinctly in the formation of each new indi- 

 vidual. 



To return once more to our figured example (PI. VIII. fig. 2), 

 it is evident that the offspring is still firmly united to its 

 parent, even by the possession of a common intestine, although 

 it is already completely filled with mature ova. This observa- 

 tion, however (as indeed has already been indicated by Krohn), 

 contradicts the assertion of Frey and Leuckart that the new 

 individuals produced by gemmation, so long as they remain 

 inserted in the common stock, do not attain such a degree of 

 development as to render them capable of the production of 

 ova. 



Lastly, as regards the third point to be elucidated, namely 

 the establishment of Autolytus prolifer as a species, I must 

 admit that I was at first inclined to think that in the animal 

 figured in PI. VIII. fig. 1 I had a new species before me. This 

 was due in part to the insufficiency of the specific description 

 oi Autolytus prolifer and the want of accurate figures*. On 

 further comparison, however, I cannot resolve upon the esta- 

 blishment of a new species, but rather believe that my animal 

 coincides with Autolytus prolifer. I also think I may say, 

 ivith probability^ that Autolytus cornutus of Agassiz is likewise 

 identical with ^.j9ro?/;^r; at least, neither from his descrip- 

 tion nor from his figures (which certainly are not sufficient for 

 specific determination) have I been able to find any essential 

 differences between A. cor7iutus, A. prolifer , and my own 

 specimen. What Agassiz says {I. c. p. 391) as to the differ- 

 ences in the number and form of the segments and in the 

 number of the long simple bristles, between the progeny of 

 Autolytus cornutus and prolifer {Sacconereis helgolandica), ap- 

 pears to me to be by no means sufficient for establishing specific 

 distinction between the primary individuals, as, from the above 

 statements with regard to number of segments &c., the pro- 

 lificate progeny not only may, but frequently even must, ne- 

 cessarily, differ from each other in these respects. 



It is otherwise with the male progeny of an Autolytus known 

 under the name of Polybostrichus longosetosus^ QErst., which in 

 all probability represents a species distinct from A. prolifer^ as 

 the accurate investigations of Keferstein established the exist- 

 ence of essential differences, in the structure of its head &c., 

 from Folybostrichus Miilleri {Sacconereis helgolandica) ^ the 

 male progeny oi Autolytus prolifer. 



* Excellentas O. F. Miiller's figure of his Nereis prolifer- (Zool. Dan. 

 fasc. ii. tab. lii. fig. 6) is for that time, it does not suffice for specific 

 determination. 



