lOG Dr. M. Schultze on the Development 



means obtained young Hermelke, and was enabled to follow their 

 development for a considerable time. When we possess a series 

 of similar observations, the forms discovered swimming freely, 

 whose mature state is still unknown, may be gradually deter- 

 mined. Thus, 11. Leuckart remarks*, that the larvae represented 

 by Busch, ' Beobachtungen,' &c. tab. 7. figs. 5, 6, which were 

 taken u}) from the open sea, remind one of the young Hermella 

 just mentioned, by their long stiff bristles. But in this case it 

 cannot be supposed that the former are actually the progeny of 

 Hermella, as the latter, according to Quatrefages, lose their cilia 

 before the appearance of any segmentation of the body. 



Our knowledge of the development of the Annelida has also 

 been advanced by the circumstance, that certain branchiferous 

 worms bear their eggs about with them until the evolution of 

 the young. Thus, in Eunice sanguinea, according to Koch, the 

 young are brought to maturity in the cavity of the body of the 

 mother, where they are retained until they reach a length of 

 from one to two inches, and acquire from 100 to 120 segments. 

 No trace of cilia appears to exist in these young animals. The 

 progeny of Nereis diversicolor quit the cavity of the mother at a 

 much earlier stage of development. In female specimens of this 

 Annelide taken in April on the coast near Greifswald, where it 

 is very abundant, I observed that the oval or pyriform embryos, 

 which are uniformly covered with cilia, and, from their reddish- 

 yellow colour, remind one of the young of Medusa aurita, came 

 in hundreds out of small apertures on the sides of the body, 

 under the pedal tubercles. These embryos (PI. II. figs. 11 & 12), 

 which swim about rapidly, measure y q th to ^th of a line ; they 

 are rather opake, in consequence of the numerous fatty vitelline 

 granules imbedded in the body. They swim with the narrow 

 end forwards, and the little animal constantly turns on its axis. 

 Near the anterior extremity is the mouth, marked out by longer 

 cilia arranged in a circle, and from this a canal passes inwards, 

 the hinder extremity of which did not appear to be formed. 

 In front of the mouth there are one or two dark eye-spots, 

 without refractive bodies. I did not observe any further meta- 

 morphosis, as the larvae soon died in my glasses. 



Instead of the cavity of the body, the embryos of other Annelida 

 are developed in peculiar sacs situated on the dorsal or ventral 

 surface of the mother, where they generally attain a propor- 

 tionably high development. This is the case in Sacconereisf, 



* Jahresbericht, 1848-53, and Wiegmann's Arcliiv, 1855, i. p. 21. See 

 Annals, 2nd Scries, xvi. p. 264. 



t Sacconereis hdgnlandica has recently been ascertained by Krolin 

 (Miiller's Archiv, 1855, p. 489) to be the result of the division of Autolytus 

 prolifer, a great step in the history of the development of this interesting 



