OJF LOST PARTS IN TUE NEMEJiTEANS. 253 



elongated both behind and before the commissures. In some 

 there are now eye-specks in the latter region, and there is a dis- 

 tinct channel leading inwards to the enlarged proboscis ; the 

 ganglia are approaching the normal shape, and the cephalic pits, 

 with their apertures leading into the posterior end of the ce- 

 phalic fissures, are well marked. The alimentary tract has as- 

 sumed a rounded form behind the ganglia, with the mouth (w) 

 in the usual position. In those best developed (e. g. fig, 5, 

 Plate VII.) the first or oesophageal division of the canal had be- 

 become differentiated from the succeeding portion; and in the 

 ordinary fragments it was apparent that the former consisted, for 

 the most part, of new texture. Such examples, however, have iiot 

 always eye-specks. The circulation now scarcely differs from 

 that in the adult. 



The motions of the animal, with a reproduced head (fig. 5, 

 Plate VII.), are not so active as those of young Borlasians usually 

 are, and they are at once distinguished by the pointed nature and 

 pallor of their snouts. 



The reproduction of a head in Linens loncjissimus has not yet 

 been observed, though the anterior end of the cicatrix of a frag- 

 ment is always the larger. It is to be remembered, also, that 

 tlie conditions under which the animals were kept were most 

 unfavourable ; for they were at a great distance from the sea- coast, 

 had no food (except what they might obtain from microscopic 

 animals or fragments of their own bodies), and had a very limited 

 supply of salt-water. Very serious wounds made in removing the 

 proboscis are easily repaired, without leaving a trace of the in- 

 jury after the pigment is fully developed in the cicatrix. 



EXPLANATION OP THE PLATE. 

 Plate VII. 



Fig. \. Anterior end of a fragment of Borlasia octoctUata about three weeks 

 after rupture : a, terminal aperture ; d, cutaneous layers. X about 

 40 diam. 



Fig. 2. Posterior end of the same fragment, similarly magnified : z, anus. 



Fig. 3. Anterior end of a fragment in a more advanced condition : a', develop- 

 ing proboscis ; h, indication of ganglia. 



Fig. 4. Anterior region of a complete, or nearly complete, animal developed 

 from a fragment : j, oesophageal division of the alimentary canal ; 

 m, cephalic pit &c. ; w, mouth. The other letters as before. 



