GALLOWAY: NON-SEXUAL REPRODUCTION IN DERO VAGA. 125 



The ingrowths between the ventral and lateral muscle bands give rise, 

 in each of the four cephalic segments of the posterior individual, to a 

 pair of ventral bristle sacs, and to the ectodermal part of the nephridial 

 organs. There are no dorsal bristle bundles formed in the cephalic 

 segments of the posterior zooid. 



The fate of the proliferation between the dorsal and lateral longitu- 

 dinal muscle bands is more obscure. The circumuesophageal connective, 

 in running from the brain ventrally, passes, as has been said, between the 

 main portion of the dorsal muscle baud and the lateral part of it, which 

 is thereby split off from the main band. In its further course ventrad, 

 the connective again returns to a position inside the longitudinal mus- 

 cles. This it does by running inward between the split off portion of the 

 dorsal band and the lateral band of muscles, so that no part of the lateral 

 muscle band ever lies inside the connective. It is perhaps significant 

 that the cells of the lateral line make their appearance in the same 

 space between the dorsal and lateral muscle bands (Plate 1, Figs. 6, 7 ; 

 Plate 2, Fig. 10, iprf. and cl. In. /.). The two sets of nervous structures, 

 — the circumcBSophageal connective and the lateral line cells, — if the 

 latter are really nervous, are thus apparently in relationship by their 

 proximity. It is, furthermore, possible that the cells which push in 

 and go to form the brain do so here rather than at the more dorsal 

 position previously noted. The fact that the whole ectodermal arc periph- 

 eral to the detached portion of the dorsal band is very much thickened 

 would seem to support this view. In this event, we should be compelled 

 to admit that the future nervous elements produced at this place 

 grow dorsally in a position peripheral to the cut off portion of the dorsal 

 longitudinal muscle band, between which and the rest of the dorsal band 

 they pass into the body cavity. This would help to explain the course 

 taken by the fibres of the connective in uniting the brain and sub- 

 pharyngeal ganglion. It would also connect the brain in its origin with 

 the lateral line system, rather than with the ventral chain, the con- 

 nection with the latter being an altogether secondary one. However 

 this may be, the course of the nervous connective is associated with the 

 position of the lateral line cells in a very suggestive way. I am as yet 

 unable to state what, histologically, the origin of the connective fibres 

 may be. From analogy with other annelids we should expect them to 

 arise from the cells of the brain, or possibly from the subocsophageal 

 ganglia, or both. The course of the connective is shown semi-dia- 

 gramnjatically in Figure 10, corCt. crc'ce. 



In the anterior zooid the course of development is somewhat different. 



