174 Dr. E. Greeff on Autolytus prolifer. 



satisfactorily account for the observations previously made by 

 Quatrefages upon the latter*. A further step in the natural 

 history of Autolytus was furnished by Max Mullerj" in his 

 excellent observations on Sacconereis helgolandica, although 

 the genetic connexion between Sacconereis and Autolytus re- 

 mained unknown to him. It was again KrohnJ who correctly 

 recognized and established the connexion between these two 

 animals^ and showed that the male and female individuals of 

 Sacconereis helgolandica observed by Max Mtiller were merely 

 the freed male and female huds o/ Autolytus prolifer. In the 

 same year (1855), and independently of Max Miiller's state- 

 ments, P. H. Gosse§ also described Sacconereis, and indeed 

 its male form, to which that observer gives the new name of 

 Crithida thalassina. 



For a very detailed memoir, published in the year 1862, 

 upon the natural history and, especially, the sexual relations 

 and development oi Autolytus, we are indebted to Agassiz||, 

 who, however, on the whole only carried further the notions 

 already expressed by Krohn, especially with regard to the 

 connexion between Autolytus and Sacconereis, but also proved 

 that the genus Polybostrichus, founded in 1843 by (Ersted^, is 

 likewise only a male bud of Autolytus, and therefore identical 

 with the male Sacconereis helgolandica of M. Miiller** and 

 with Crithida thalassina of Gosse. Agassiz, moreover, was the 

 first who observed the brood of the sexual buds of Autolytus 

 and their development into the primary individuals, and thus 

 filled up what had previously been an important gap. Never- 

 theless, notwithstanding the great amount of material pre- 

 sented by him, he still remains in many respects behind Krohn 

 as regards the accuracy and clearness of his observations. The 

 generic characters so distinctly pointed out by Krohn for Au- 

 tolytus especially have not been duly noticed by Agassiz : thus, 

 for example, the characteristic elegant circlet of little pointed 

 teeth which crowns the entrance into the tortuous oesophagus is 



* Comptes Rendus, August 1843, and Annales des Sci. Nat. 1844, 

 tome i. p. 22. See also the subsequent more detailed treatise upon Syllis 

 prolife7-a, " Memoire sur la Generation alternante des Syllis" in Ann. Sci. 

 Nat. ser. 4. tome ii. p. 143, pi. 4. 



t MUUer's Archiv, 1855, p. 13, pis. 2 & 3. % Ibid. 1855, p. 489. 



§ Ann. & Mag. Nat. Hist. ser. 2. vol. xvi. p. 305, pi. 8. fig. 5. 



II *' On Alternate Generation in Annelids, and the Embryology of 

 Autolytus cornutus" Boston Journ. Nat. Hist. vol. vii. p. 384, pis. 9, 10, 

 & 11. 



^ Gronland's Annulata Dorsibranchiata, p. 30, pi. 5. fig. 62. Copen- 

 hagen, 1843. 



** The identity of Sacconereis and Polyhosti-icJms was indicated in the 

 same year, and apparently before Agassiz, by Keferstein, ' Zeitschr. fiir 

 wiss. Zool. Bd. xii. p. 113, pi. 11. figs. 1-6. 



