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•,i\>v. 6>/ Arenicolapiscatorum. 107 



according to the observations of Johann and Max Miiller, and of 

 myself, in Cystonereis, Kolliker, Exogene, Oersted and Kcilliker, 

 and ^yllis 'pulligera, Krohn. In Sacconei^eis the young appear 

 to issue in swarms from the ventral sacs of the mother, as they 

 are provided with several bands of cilia, and when the sac is 

 artificially destroyed, possess the power of swimming in a high 

 degree ; whilst the evolution of the young of Cystonereis, Exogene, 

 and Syllis pulligera takes place on the body of the mother until 

 the disappearance of the cilia (which are certainly present in the 

 earliest stages of Exogene cirrata and Syllis pulligera) and the 

 appearance of the segments and lateral bristles. 



In a considerable number of Branchiferous Annelides, again, 

 the eggs are deposited enclosed in a mass of jelly, and develope 

 themselves in this covering, without any connexion with the 

 mother, until the young are furnished with bristles and other 

 locomotive organs like those of the mature animals. These do 

 not enable them to swim freely for any length of time, but only 

 to creep along the sea bottom. Examples of this kind occur in 

 the Tubicolar families of the Terebellacea and Serpulacea in the 

 genera Terebella and Frotula, with whose young Milne-Edwards 

 has made us acquainted. As the masses of eggs of these animals 

 are attached to the exterior of their tubes, no doubt can exist as 

 to their origin, when they are collected at the same time with 

 the mother; and the tracing of their further development is 

 extraordinarily facilitated by the fact that they require no change 

 of water, at least as long as they remain enclosed in the gela- 

 tinous masses, and therefore survive in the glasses. 



An example of this mode of development is also presented by 

 Arenicola piscatorum, the egg-masses of which I collected near 

 Cuxhaven, on the 22nd March 1852, and brought with me to 

 Greifswald, where the further development took place. On the 

 island of Neuwerk, which lies a few miles to seaward of Cuxhaven, 

 the traces of Arenicola piscatorum occur in extraordinary numbers. 

 In passing, during the ebb-tide, over a surface of sand but 

 slightly covered with water, I saw, lying on the sand, close to 

 almost every one of the little heaps thrown up by the worms 



gemmiparous worm ; and the same is probably the case with the second 

 species, S. Schultzii, from the Mediterranean, described by J. Miiller. I 

 liave no doubt that the animal of this genus taken by me at Heligoland, 

 and mentioned by J. Miiller from my letters, is identical with that observed 

 by Max Miiller (Muller's Archiv, 1855, p. 13). I took no notes of the 

 number of segments in the body ; but the young animal is represented at 

 fig. 10 (PI. II.). It represents a further step in the development of the 

 young worm represented by M. Miiller, I. c. tab. 2. figs. 5-8, and is par- 

 ticularly distinguished by its four bands of cilia. Of the fine cilia which 

 at an earUer period covered the whole body, only those on the head are 

 still in existence. 



