56 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Central Nervous System of Lumbricus.* — Herr B. Friedlander Las 

 investigated the minute structure of the central nervous system of the 

 earthworm. As Faivre correctly stated, though he has been contradicted 

 by Vignal, the short connectives between the closely applied ganglia of 

 the ventral cord lie in front of the points of origin of the single nerves. 

 In each ganglion there are a limited number of large, multipolar ganglion 

 cells which are constant in position and have a peculiar chemical con- 

 stitution ; they are probably comparable to the median cells described 

 by Hermann in Hirudo and by Kiikenthal in Travisia. In each ganglion 

 there are fibrous transverse bridges at the level of the point of origin of 

 the nerves. With the exception of the first root of the double nerves, 

 the lateral nerves have their fibres partly related to these transverse 

 bridges; the first root of the double nerves has a more ventral, the 

 second a more dorsal origin. There is in Lumhricus a median nerve 

 running between the two chief cords of fibres. In each of these latter 

 there are three groups of closely approximated, well-developed nerves ; 

 in the ventral group there is a specially thick nerve-tube. Near this 

 last there is a differentiated tissue similar to the fibrils of the brain. 



The sub-oesophageal ganglion is probably the product of the fusion 

 of two ventral medullary ganglia. The investments of the neural canals 

 are purely of the nature of connective tissue and are not to be compared 

 to the myelin of the nerves of Vertebrates. They probably have, as a 

 subsidiary function, the duty of preventing lesions of the ventral cord, 

 on the contraction of the worm. The contents of the neural canals 

 consist of processes of ganglionic cells which are probably fused with 

 one another into a homogeneous mass. Tlie two lateral neural canals 

 begin at the hinder end of the ventral cord in the form of processes of 

 two ventrally placed ganglionic cells of special character, but not of 

 unusual size ; in their further course they take up the processes of other 

 ganglionic cells of similar character. Before their entrance into the 

 neural canals the processes form complicated anastomoses with one 

 another, as well as with the median canal. The nervous central sub- 

 stance of the brain differs essentially from that of the ventral cord. The 

 proximal ends of the anteriorly directed nerves have a deposit of 

 numerous small ganglionic cells which form the lobes of the brain. In 

 more posterior transverse sections a fine fibrillar dotted substance placed 

 centrally and ventrally and ganglionic cells may be seen. In sections 

 stained with carmine, scattered nuclei of connective tissue which indicate 

 the presence of a neuroglia-like supporting substance, may also be made 

 out. 



The ganglionic cells may be divided into several sets; the whole 

 dorsal part of the brain consists of a cortical layer chiefly made up of 

 ganglion-cells ; these are remarkable for the difficulty with which they 

 can be preserved, and it was quite impossible to make out the number of 

 their processes. Most of them are very small, but some are larger, pyri- 

 form, and unipolar. There are, further, groups of large pyriform cells, 

 and cells with extremely sharp contours, and very broad processes ; the 

 latter form a dorsal and a ventral fibrous cord, which only unite into 

 one a short distance in front of their entrance into the oesophageal com- 

 missures. There appears to be here a complete crossing of the fibres. 



The nervous central substance or dotted substances of Leydig 



* Zeitschr. f. Wiss. Zool., xlvii. (1888) pp. 47-84 (2.pls.). 



