o/ Arenicola piscatorum. 109 



cilia, whilst the following ones are at first rather close together 

 (fig. 5), but gradually become more distant with the further 

 growth of the animal (fig. G). The body, which hitherto had 

 been quite opake, now separated into a lighter peripheric por- 

 tion, lying under the skin, which still continued rather dark, 

 and an opake central portion. The former represents the cavity 

 of the body, the latter the intestine, in which a cavity may be 

 recognized by the granules which move about in it. The intes- 

 tinal canal does not, however, lie free in the general cavity, but 

 is attached to the inner surface of the skin by annular bands 

 corresponding in number with the developed segments of the 

 body. A mouth exists behind the eyes, on the ventral surface ; 

 the anal opening occupies the extreme hinder end of the body. 

 No traces of a nervous or vascular system are perceptible. 



On the twentieth to the twenty-fourth day the bands of cilia 

 disappear entirely, and the young animals, which had previously 

 moved slowly about in the gelatinous mass, now quit it in the form 

 of sluggish, helpless worms. Their length is now ~ to |"'. Their 

 form is cylindrical, somewhat widened towards the anterior ex- 

 tremity, which terminates in a point, and truncated behind 

 (fig. 7). The mouth lies close behind the red eye-spots, which 

 are destitute of a refractive medium ; it leads into a muscular 

 oesophagus [a), and this into the intestine, which runs straight 

 backwards to the anus. The number of segments in the body- 

 has increased to 10 or 12 by additions at the hinder extremity 

 (between the last and penultimate segments). On the most 

 anterior of these the first lateral bristles are perceptible, standing 

 in groups of from two to four; they are delicately serrated on 

 one edge (fig. 9), in this respect resembling the inhnitcly larger 

 bristles of the mature Arenicola. 



My endeavours to keep these young worms any longer failed 

 entirely. I put them into a glass upon a thin stratum of sand 

 which I had brought with me from the island of Neuwerk, con- 

 taining a variety of Infusoria and Algpe which might possibly 

 have served them for nourishment, but they died without under- 

 going any further change of form. I think, however, that I 

 saw indications of the formation of the auditory vesicle, as I ob- 

 served on each side, in front of the eyes, a small vesicle with a 

 tolerably sharp outline, and with irregularly granular, but not 

 calcareous, contents, which would probably afterwards be the 

 otolithes. 



It is to be expected that the young Arenicola, after creeping 

 out of their gelatinous envelope, would bore into the sand in the 

 neighbourhood of their parents, and then gradually acquire their 

 mature form. The next thing to be done, therefore, is to seek 

 the young in this situation at the proper season. 



