958 SUMMARY OF CURRENT RESEARCEffiS RELATING TO 



off processes, in part to the nerves, in greater part to the longitudinal strand 

 of the opposite sidej and to a small extent to the longitudinal strand 

 of the same side. The differentiation of ganglia and connecting com- 

 missures is not yet complete. Each complex of nerve-cells, the processes 

 of which form part at least of each pair of nerves, is to be regarded as a 

 ventral ganglion. There are four pairs of aggregates in each group, two 

 lateral and two internal, two ventral, and two dorsal. As a portion of the 

 processes of the lateral cells passes to the other side, two bridges are 

 formed, one ventral and one dorsal. In each segment there are two or 

 three such double bridges, and corresponding to these two or three pairs of 

 nerves passing out from the same plane. 



The strands surrounding the gut have the same structure. On their 

 lower portion lies a ganglion, which in structure corresponds to half of a 

 ganglion from the ventral cord. The same groups of cells are present 

 except the median internal. Since the strongly developed sympathicus 

 springs from this oesophageal commissure, the latter may be termed the 

 stomatogastric centre. 



The brain exhibits three pair of ganglia. Into both brain and ventral 

 cord ectodermic elements enter. The upper surface of the brain exhibits a 

 group of large round cells, possibly remnants of the apical plate of the 

 larva. 



The free-living forms (Armandia, Polyofhihalmus) have a perfectly 

 developed brain, while the ventral cord is still associated with the ecto- 

 derm; those creeping in the mud (especially Travisia) have the ventral 

 nerve-cord completely separate from the ectoderm, but a reduced brain and 

 sensory system. The memoir concludes with a comparison of Opheliaceae 

 and Archiannelids. 



fl. Nemathelmintlies. 



Anatomy of Gordiidse.* — M. A. Villot is of opinion that Prof. 

 Vejdovsky would have avoided some of the errors into which he has fallen 

 with regard to the structure of the Gordiidae, if he had made sections, had 

 been able to examine the worms in the fresh state, and had a knowledge 

 of their larval development. The French author has lately been so 

 fortunate as to get examples of the parasitic stage of G. violaceus, which is 

 passed in the abdominal cavity of Procrustes coriaceus. 



The resemblance of the rings of the integument of embryos and larvse 

 to the segmentation of Annelids is apparent only, for they are merely due to 

 folds of the integument. The fibrillar and nervous nature of the hypodermis 

 is maintained, but M. Villot finds he was wrong in regarding the so-called 

 nuclei as having any relations to the fibrillar elements ; they are vascular 

 organs which are connected with the pores of the epidermis and the 

 aquiferous canals which traverse the dermis. To understand the origin 

 and histological significance of the elements of which the integument is 

 composed, it is necessary to study them in the parasitic larvae before the 

 formation of the dermis. Beneath the epidermic cuticle, there is a layer 

 of embryonic cells, which, seen from above, is very like a pavement- 

 epithelium ; in each cell there is a large nucleus which stains well with 

 carmine ; on making a longitudinal section, it is seen that these embryonic 

 cells have their protoplasm formed of developing fibrils, while their nucleus 

 becomes vesicular and gives off at each pole a tubular prolongation ; the 

 ventral plexus and the central nervous s;,stem are only a special develop- 

 ment of the fibrillar elements of the hypodermis, and the author was, 

 therefore, wrong in previously ascribing to them a mesodermal origin. 



* Ann. Sci. Nat.— Zool., ii. (1887) pp. 189-212. 



