512 Mr. C. K. Navayana Eao on the Anatomy of 



deposit of vitellin globules, and in the more advanced stages 

 of degeneration the nucleus also is indistinguishable, and the 

 modifying cytoplasm may be stained in certain areas of 

 the cell-body, which represent yolk-nucleus. The cell-wall 

 now degenerates also, and the mass of globules of yolk is 

 lield together only by an excessively thin pellicle, which 

 breaks on the application of the slightest pressure. 



The Nervous System. — Anotiier feature of the anatomy of 

 this species of earthworm that is really noteworthy is the ex- 

 tremely generalized structure of the nervous system (PI. XVI. 

 figs. 6, 6«). The nerve-cord is composed of two lateral bundles 

 of fibres and cells, with clear fairJy broad median hyaline 

 space not occupied hy any tissue elements. It is easily noticed 

 by the naked eye that this median space is grey, and is thus 

 distinguishable from the white bundles on either side. 

 Among the fibres present in each division of the cord two 

 kinds are distinguishable, viz., the axons of neurons and the 

 giant fibres which are not traceable to any cells. The latter 

 are laid in four bundles in the cord, two marginal and two 

 internal sets. The internal bundles lie on both sides of the 

 median dividing hyaline space. There are no ganglionic 

 swellings in any part of the cord, which is of uniform thick- 

 ness throughout. The nervous system of this species is 

 almost ideally constructed for the study of the details of the 

 structure of the cells and fibre-connections, and a slight 

 teasing and suitable staining with methylin-blne will 

 unravel the intricacies of the nerve-paths far too difficult 

 to be made out by a similar process in the other species of 

 earthworms. In paraffin sections the excessively thin 

 ccelomic epithelium is found to form an investment of the 

 dorsal half of the cord only, the histological elements are 

 seen grouped on either side of the clear median space, and 

 interstitial spaces are occupied by a granular substance. 

 The granular mass must be in the nature of a matrix, which 

 together with the giant fibres and the muscular fibres must 

 help to bind the cells together. The hyaline membrane 

 forms the outer layer which, in the processes of imbedding, 

 usually breaks in all directions, appearing under magni- 

 fication like a network of fibrils. In so far as the two 

 lateral bundles remain apart the nerve-cord is a primitive 

 structure, but as regards its cytological contents it does not 

 appear to be so. Numerous kinds of cell-bodies are distin- 

 guished in the stained entire cord, and follow a strict law as 

 regards their position througliout the cord and also in 

 the oesophageal ganglia. Mention must be made of the 

 strikingly large spherical cells which I term " Central Cells," 



