90 SUMMARY OF CURRENT RESEARCHES RELATING TO 



directly with the membrane, separating the cellular from the fibrillar 

 portion of the cord. Posteriorly the vessel is quite isolated, and the 

 anterior association afterwards disappears ; but there seems thus to be a 

 special provision for nourishing the nervous system during its development. 



6. Vascular system. — By arrangement of the dorso-ventral muscles two 

 longitudinal partitions are formed in the body. The ovoid median sinus 

 thus formed contains the nervous system, the ovaries, the two blood-vessels, 

 the anterior and posterior portions of the mid-gut. The lateral prolonga- 

 tions of the digestive system and the testes lie in the marginal sinuses. 

 The dorsal and ventral vessels are very different. Two solid cellular strands 

 are formed along the alimentary tube, the one in the median ventral, the 

 other in the median dorsal line. Both seem to arise from the splanchnic 

 layer of the mesoderm. Each strand is differentiated into a central cord, 

 and an external layer separated from the former by a delicate structureless 

 membrane. The external layer forms the wall of the blood-vessel, the 

 central strand forms the elements within. 



7. A temporary dorsal organ is for the first time noted. It lies in the 

 dorsal middle line, in the anterior third, and consists of a canal running 

 into an external prominence from which long delicate threads are emitted, 

 probably for fixing purposes. 



8. General conclusions. — Nusbaum notes the accordance of his results 

 with those of Salensky on BrancMohdella, and compares his conclusions 

 with those of others. As to the position of the Hirudinea, his embryo- 

 logical results lead him strongly to maintain Balfour's opinion that they 

 were slightly degenerate Annelids, near allies of the Chsetopods. 



Colossal Nerve-fibres of the Earthworm.* — Prof. F. Leydig, after 

 referring to the views of other anatomists, gives an account of his own 

 re-examination of the colossal nerve-fibres of the ventral ganglionic chain 

 of the earthworm. They may present a quite homogeneous interior, even 

 after treatment wdth reagents, and, again, with certain hardening fluids such 

 as chromic and acetic acid they may exhibit certain differentiations. 



A band of granular axial substance is seen in transverse sections, in 

 which the granules have an angular form, and it is possible to convince 

 oneself that there is an extremely fine plexus, in which the dots are the 

 nodal points. There is, therefore, a spongioplasm, in the meshes of which 

 a hyaloplasm is contained. 



It seems that, in transverse sections, the median or larger of the 

 colossal fibres is divided by septa arising from the cortical layer into two 

 halves, each of which has its own axial bands. This is clearly the com- 

 mencement of what in other genera is the absolute division of the fibre into 

 two tubes (e. g. Stylaria). Careful observation reveals the presence of 

 intermediate stages between the ordinary and the colossal fibres ; this is 

 best seen in the region of the ganglia. 



The author directs attention to the relations between the colossal fibres 

 and what he has already taught as to the structure of the nerves of inverte- 

 brate animals. To understand thoroughly the nature of the colossal fibres 

 it is necessary to extend investigations to the Arthropoda, where likewise 

 there are colossal fibres, which are true elements of the nervous system. 



Annelids of the Genus Dero.j — Mr. E. C. Bousfield points out that 

 the species of Dero are distinguished from the Naides by the absence of 

 eyes, of corpuscles from the perivisceral fluid, and by the termination of 



* Zool. Anzeig., ix. (1886) pp. 591-7. 



t Eeport Brit. Assoc. Adv. Sci. for 1885 (188G) pp. 1097-8. 



