THE EARTHWORM. 49 



PLATE XI. 



THE EAKTHWOEM. THE EXTERNAL CHARACTERS. THE ALIMENTARY CANAL AND ITS 



APPENDAGES. THE EXCRETORY ORGAN, ETC. 



pio. I. Dorsal view of the anterior end of the body of a sexually mature worm. 

 The zonitic markings, zn., may often be more than one in number for each segment, 

 especially in the generative region.* 



FIG. II. Ventral view of a portion of the same. 



FIG. III. Ventral view of the terminal segments of the same, the anus slightly 



upturned. 



Figs. I. to III., all x 2. 



FIG. IV. Ventral view of the first seventeen segments, after removal of the cuticle ; 

 a portion of the integument of the left side has been pinned out, to show the openings of the 

 spermathecae. 



The apertures of the segrnental organs are not indicated. (Compare Fig. V., 

 Plate XII.) x 3. 



FIG. V. The same, seen from the left side. 



Either spermatheca may open by two apertures, as did the hinder one in the specimen 

 figured, x 2. 



FIG. VI. Two setse, drawn to the same scale. 



The right hand one is from the genital region, and the left from a postgenital segment. 

 : Indicates an axial differentiation. A. 3. 



FIG. VII. A small portion of the cuticle, with the cuticular sheath of a seta. 

 * These refractive dots appear to be due to the presence of enclosures. D. 3. 



FIG. VIII. The alimentary canal exposed from the dorsal aspect, its roof having been 

 subsequently removed on the right side, x 2^. 



The two hinder pairs of calciferous glands may often be absent, and the mesenteric septa 

 in the crop-gizzard region are subject to variation, t 



* In this and the following plate, the numbers of important segments are indicated wherever desirable in small 

 Arabic numerals. 



f The brownish-yellow tissue, usually termed liver, has no direct connection with the lumen of the alimentary canal. 

 It is always associated very largely with the blood-vessels, and is in all probability a direct derivative of their walls. 

 It appears to be active in the production of some constituent of the blood, similarly to that tissue described by 

 Lankester in the Leeches as vaxifacticr. See Lankester " On the Vasifactive and Connective Tissues of the Medicinal 

 Leech," Q. J. M. S., vol. xx., 1880. Also papers by Weldon on the Vertebrate Kidney and Supra-renal bodies, 

 the same journal, vols. xxiv. and xxv. I have observed, in cells of the alimentary epithelium teased up shortly after 

 death, the presence of ini/estfil particles of decomposing vegetable matter. In the absence of true digestive glands, and 

 of any knowledge of the physiology of alimentation in this animal, the probability of an intracellular digestion of this 

 solidly ingested food material must not he overlooked. (Compare Hydra, PI, xvii,, fig. v., et se<j.) 



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