288 THE ANATOMY OF INVERTEBRATED ANIMALS. 



cate, is seen to skirt its inner contour. The hairs, projecting 

 inward, come into close contact with the solid particles sus- 

 pended in the mucous fluid. 



A nerve may be traced accompanying the antennulary 

 nerve to the sac, and appears to be distributed principally 

 along the setigerous band, so that the extremities of the 

 nerve fibrils come into close relation with the bases of the 

 hairs. Some, if not all, of the sandy particles are insoluble 

 in strong acetic acid, and would appear to be siliceous.^ 



Two glandular sacs commonly known as the green glands^ 

 which were formerly regarded as the auditory organs, lie in 

 the cavity of the head. An aperture is visible on the inner 

 or oral side of a conical prominence, upon the inferior portion 

 of the coxal joint of the antenna. A bristle passed into this 

 aperture enters a large but very delicate and transparent 

 sac, filled with a clear fluid, which is usually conspicuous on 

 each side of the anterior end of the stomach, when the cara- 

 pace is carefully removed. A nerve which comes ofi" from 

 the cerebral mass close to the antennary nerve, passes to the 

 neck of this vesicle, and is distributed over its surface be- 

 tween the outer and inner membranes, of which it is com- 

 posed. Inferiorly the vesicle rests upon a large greenish, ap- 

 parently glandular mass, but is directly connected with the 

 latter only at two points, firstly by a vascular cord, which 

 passes to the central and usually more yellow portion of the 

 gland, and secondly by a short neck-like continuation of the 

 sac itself, which is attached over a small circular space, mid- 

 way between the centre and the periphery of the gland, and 

 opens into the circular principal duct of the gland. There is, 

 therefore, a free communication between the cavity of the 

 gland and the exterior by means of the sac, which is, in this 

 respect, simply a dilated duct. A section of the gland shows 

 it to be composed of two subtances, a central and a cortical. 

 The latter is composed of minute caeca, filled with a homo- 

 geneous gelatinous matter, containing many large nuclei ; 

 the former is traversed in all directions by large canals, so as 

 to have a spongy appearance. The Cc^ca open into the ulti- 

 mate ramifications of the canals, and the spongy, lung-like 

 texture of the central mass seems to arise merely from the 

 very free anastomosis of their larger branches, which event- 



* See^ for a full account of the minute structure of the auditory organs in 

 the higher Crustacea, Henseu's " Studien iiber das Gehororgan der Decar 

 poden," 1863. 



