On the Development of Arenicola piscatorum. 105 



XIII. — On the Development of Arenicola piscatorum; with 

 Remarks upon that of other Branchiferous Annelides. By Dr. 

 Max Schultze*. 



[With a Plate.] 



Most of the Branchiferous Annelida, of which the earliest forms 

 have yet been observed, leave the egg-capsule or the embryonic 

 receptacle of the mother in a condition by which they are enabled 

 to swim about freely. They ai-e furnished with strong bands of 

 cilia, or with a uniform ciliary coat, so that they can roll about in 

 the water at pleasure. 



By fishing with a fine net in the neighbourhood of the coast 

 or on the high sea, a considerable number of such roving An- 

 nelidan larvae come to the hands of the zoologist. As these, 

 without exception, when in their earliest stages of develop- 

 ment, possess a \evy different form from their parents, and are 

 destitute of any organs by which the determination of their 

 origin might be rendered possible, a long series of investigations 

 upon their further evolution is necessary to obtain certain indi- 

 cations of their parentage. It is rarely that such larvae can be 

 kept alive in the experimental glasses long enough to enable us 

 to follow their further metamorphoses upon one and the same 

 individual. Naturalists have therefore generally been compelled 

 to confine themselves to collecting the different young forms of 

 the same animal one after the other, by repeated fishings, and 

 uniting these to form a general picture of the development. 

 Frequently however it happens that, notwithstanding constant 

 exertions, a form once observed never again comes into the net, 

 or occurs so rarely, that the origin of the single larvse has 

 remained unknown, whilst others which were taken plentifully 

 and at different periods continued so obstinately in a certain 

 early stage of development, that all endeavours to ascertain their 

 subsequent fate were vain. It is therefore not to be wondered 

 at if, amongst the great number of young Annelides which have 

 been fished up from the sea and described, there are but few 

 which we can refer to their parents. A remarkable example how, 

 with the greatest perseverance, the goal is often reached only 

 after the lapse of a long period, is furnished by the Mesotrocha 

 sexoculata, recently ascertained by Max JMiiller to be the larva 

 of Cheetopterus, although J. Miiller and Busch were repeatedly 

 led to investigate it during their excursions without being able 

 to observe any considerable progress in its development. 



The employment of artificial impregnation will be of import- 

 ance to the study of the metamorphoses of the Annelida. As 

 yet this has only been tried once by Quatrefages, who by this 



* From the Abhandl. tier natiuforsch. GescUsch. in Halle, vol. iv. Cotn- 

 muuieated by the Author and translated bv W. S. Dallas, F.L.S. &c. 



