SYSTEMATIC POSITION OF A GiaANTIC EARTHWOEM. 73 



consists of two rows of cells termed respectively the " untere " and " obere Saulenregion ;" 

 below this, again, is a vascular la5'er. 



Drs. Horst and v. Mojsisovics interpret the structure of the clitellum differently. 

 According to them the hypoderm layer becomes modified in the region of the clitellum ; 

 its cells are considerably longer than elsewhere, and have taken on a glandular cha- 

 racter ; below these is another layer of cells, which are distinguishable from the upper 

 layer by their larger size, shape, and less granular contents ; the upper row of cells 

 corresponds therefore to the hypoderm plus the " obere Saulenregion " of Claparede, 

 while the lower layer corresponds to the " untere Saulenregion." 



The figures of transverse section of the clitellum given in Dr. von Mojsisovics's paper 

 are not really so very different from those of Claparede, and it is, indeed, difficult to 

 understand why the latter should have insisted upon the distinctness of the hypoderm 

 layer from the " obere Saulenregion," inasmuch as h.eji(jures the cells of the two regions 

 in some cases in actual contact, and, indeed, hardly indicates a septum of division at any 

 point. It is a curious fact that the ultimate branches of the blood-system only reach 

 halfway up to the outer layer of cells, and terminate precisely where, on Claparede's 

 hypothesis, is the line of division between the hypoderm and " obere Saulenregion," and 

 it is very possible that this fact caused Claparede to distinguish them. 



A transverse section through the body-wall of Microchoeta, in the region of the 

 clitellum, is represented in fig. 8 of PI. XV. The epidermis of the general body-surface 

 is here unmodified ; it is quite impossible to distinguish the cells which form the 

 epidermis of the clitellum from those which are found elsewhere ; the same narrow 

 columnar cells, each with an oval nucleus situated near the lower end of the cell, form 

 the chief part of the tissue, vs^hile here and there a larger granular cell occurs. The 

 resemblance is in fact so complete that 1 have not thought it worth while to reproduce 

 the epidermis of the general body-surface in another figure. 



The epidermis layer [e) is of course covered by the chitinous cuticle (c), and is 

 bounded below by a stout membrane, which sends off prolongations both from its upper 

 and lower surface ; the former pass upwards between the epidermis-cells and are no 

 doubt similar to the "processes of pigment-cells belonging to the connective-tissue 

 system " which make their way among the epidermis-cells of Lunihricus as described by 

 the above-mentioned writers, as also by Prof. Lankester' (in the Leech). Beneath 

 the epidermis is the glandular layer of the clitellum {gl) ; the glandular cells of this 

 are imbedded in a network of connective tissue continuous with the membranes which 

 separate the glandular from the hypodermic layer. The structure and arrangement of 

 these glandular cells, again, appear to be different from that characteristic of Lumhricus. 



In the latter the cells are arranged in a regular fashion in double rows, separated 

 by septa of connective tissue. In Microchceta the glandular layer of the clitellum is 



' " On Intra-epithelial Capillaries in the Integument of the Medicinal Leech," Quart. Journ. Micr. Soo. 

 vol. XX. new ser. p. 303. 



