Structure of the Oli'gochceta. 95 



Oligochseta has by no means kept pace witli that of the 

 exotic forms of Earthworms, and a great many more facts 

 will have to be accumulated before any profitable speculations 

 can be indulged in as to the relations of different families 

 and genera. 



Tlie Zone of Growth in Urochaeta. 



More than thirty years ago a note by Fritz Miiller upon 

 " Lumhri'cus corethrurus^^ (= Urochceta hystrix, Perrier, 

 " Mdmoires pour servir a Phistoire des Lombriciens terrestres," 

 Nouv. Arch. Museum, 1872 ; and Urochceta corethrura^ id., 

 " Organisation des Lombriciens terrestres," Arch. Zool. Exp. 

 t. iii., 1874) was translated into these Annals (" Descrip- 

 tion of a new species of Earthworm," Ann. & Mag. Nat. Hist. 

 2nd ser. vol. xx. 1857, pp. 13-15) from Wiegmann's 

 'Archiv,' many of the facts in which seem never to have been 

 either confirmed or refuted. I have lately received through 

 the kindness of the authorities at Kew living examples 

 of Urochceta from both Singapore and Mauritius, thus ex- 

 tending its known range. All the examples showed a spot 

 at some distance from the tail end, distinguishable, as Fritz 

 J^Iiiller correctly pointed out, by its tumid appearance, and 

 also by the fact that the intestine here was empty of debris ; 

 this gave a whitish appearance to the part in question. In 

 preserved specimens this region was not so obvious, but could 

 be detected on a careful examination. Fritz Miiller states 

 that the skin here is devoid of bristles, and suggests that it 

 is the spot where the formation of new segments takes place. 

 I have found, by means of longitudinal sections, that the 

 bristles are not always absent, but that they are, w4ien present, 

 extremely small and easily overlooked; this suggests that 

 they are embryonic setse*. Furthermore the epidermis in this 

 region of the body is without the large oval glandular cells 

 which are so characteristic a feature of the integument in all 

 Oligochjeta. All the cells are more or less alike. This, 

 again, I take to be an embryonic feature. In the third place, 

 the intestine in some individuals was very much contracted in 

 diameter, and, as already mentioned, was empty of earth. 

 This is not so distinctly an indication that rapid growth is 

 going on. The nephridia, however, and the septa showed no 



* In the embryo of Lumbricida3 within the cocoon, fiilly-deveLjped 

 setae, but of small size, are found. These drop out and are replaced by 

 setiB of the normal size. A seta does not appear to grow in thickness, 

 but only in length ; young sette of an adult worm consist of only the tip, 

 which is as large as it ever will be. 



