198 DESCRIPTIONS OF PREPARATIONS. 



supra-oesophageal ganglion, the two cephalic provisional nephridia, and the pharynx, 

 the prostomium growing forwards by degrees. It is not separated by a furrow from 

 the buccal somite as it is in all other Chaetopoda except Chaetogastridae (see Vej- 

 dovsky, op. cit. infra, p. 162). In Typhaeus from India it is apparently absent, and 

 the mouth therefore terminal. 



In Microchaeta Rappifaz. somites are secondarily annulated, as in the Leeches. 

 The number of annuli in the first and in each somite from the ninth onwards is 

 three : but in the second to the seventh somite inclusive it is either six or seven. 



The cuticle is thin, transparent, and variable in thickness in different regions of 

 the body. It is said to consist of two layers, an outer longitudinal and a thicker 

 inner circular fibrillar layer. It is pierced by minute pores, the orifices of unicellular 

 hypodermic glands. 



The hypodermis or epidermis consists of a single layer of cells. In the inter- 

 segmental furrows they are shorter than elsewhere, and are non-glandular : whereas 

 in other regions glandular and non-glandular cells occur intermixed. The non- 

 glandular cells are either cylindrical with several basal processes, or more or less 

 globular with a slender external process and one or more basal processes. The latter 

 kind of cell lies at a deeper level than the former. The glandular cells vary some- 

 what in shape and in the nature of their contents, probably in accordance with their 

 state of activity. According to Professor Ray Lankester, processes of pigment cells 

 belonging to the subjacent connective tissue pass up, especially in L. olidus, between 

 the hypodermis cells, as in the Leech. In the clitellum non-glandular cells are not to 

 be found in the common Earthworm and some of its allies ; in others they are pre- 

 sent in reduced numbers. Its glandular cells are divisible into a more superficial 

 layer with coarsely granular contents which stain readily with carmine, and a deeper 

 layer with finely granular contents which do not stain with the same reagent. In 

 Allolobophora (Dendrobaend) rubida, Vejdowsky traced nerve-filaments into appa- 

 rent continuity with the glands. Capillaries penetrate between the clitellar glands, 

 and are very numerous in the common Earthworm : in some species they are few in 

 number. In Perionyx and Megascolex the general hypodermis is vascularised as in 

 the Leech. An elastic basement membrane separates the hypodermis from the mus- 

 cular layers of the body-wall. It is highly developed in Perionyx and Perichaeta. 



The muscles are disposed in an outer circular and an inner longitudinal layer. 

 Each muscle-fibre corresponds to a single cell with a well-developed cortical fibrillar 

 substance and a central medulla or protoplasm which is scanty, and in which 

 a nucleus has been found in Z. olidus and Phreoryctes, two worms in which the 

 fibrillar cortex is sometimes deficient at one spot, so that the muscle-cell becomes 

 coelomyarian. In L. terrestris and some other Lumbrid and a few other Earth- 

 worms, as well as in Serpula and Protula among Polychaeta, the simple layer of lon- 

 gitudinal cells found in the lower Oligochaeta is disposed in parallel folds, the bi- 

 pinnate bundles of Claparede, which are held together by intervening connective 

 tissue. The muscle-cells of the longitudinal coat in other Chaetopoda are arranged 

 in more or less regular groups or bundles. The longitudinal coat is divided in 

 Oligochaeta into distinct tracts by the projection internally of the sacs of the setae. 

 The bundles of protrusor or parieto-vaginal muscles attached to the bases of the 

 sacs in question are derived however from the circular coat. Bundles of muscular 

 or inter-follicular fibres pass from the bases of the sacs in the dorsal row to the bases 



