88 Dr. A. Krohn on the presence of two Glandular Sacs 



ring, often of a blackish colour ; it leads into a roundish sac, 

 often wrinkled in folds, situated in the cephalothorax, and 

 communicating with the orifice by a short, narrow canal or 

 neck. In many species [Cerastoma cornutum^ Phalangium pa- 

 riettnum) the two sacs immediately attract the eye, after the 

 careful removal of the dorsal shield, by their dark tile-red or 

 dark-brown colour, whilst in other species {Opilio Jiystrix^ 

 Leiobimum rotundum) they appear quite destitute of pigment, 

 and are therefore at first easily overlooked*. 



The two sacs, already noticed by that very meritorious ob- 

 server Treviranus, but erroneously regarded by him as two 

 lateral eyes, prove, upon closer examination, to be glands, the 

 intimate structure of which resembles that of many glands of 

 Insects. In the first place we may distinguish a very delicate 

 outer envelope or tunica propria^ immeshed in tracheal rami- 

 fications ; this is followed by an epithelium composed of secre- 

 tory cells, which is lined by a very transparent cuticle or in- 

 tima^ bounding the cavity of the sac and thrown into numerous 

 fine folds. This intima is continuous with the integument at 

 the exterior orifice, and consequently proves to be a greatly 

 attenuated inversion of the latter into the sac. 



The secretory cells lie close together in a single layer, and 

 contain, besides a turbid, finely granular substance, a roundish 

 nucleus, and in the vicinity of this a vacuoliform cavity, which 

 usually exceeds the nucleus more or less in size. Each cell 

 appears to be connected with the intima by an extremely fine 

 efferent canal. The presence of these little canals may be 

 easily demonstrated by the action of a weak solution of potash 

 upon the sac, by which the cells and pigment are indeed dis- 

 solved, but the canals and the folded intima are thereby only 

 brought more distinctly into view. The layer of cells may 

 be most distinctly perceived in Leiohunum. 



In Cerastoma cormitum and Phalangium parietinum^ in 

 which the sacs, as already stated, are of a dark tile-red or 

 brown colour, the pigment, consisting of very minute granules, 

 is situated between the cellular layer and the intima, but 

 seems, at least partially, to insert itself between the cells. In 

 these cases the cellular layer extends to the neck of the sac, 

 and the excretory canalicula are much longer than in Leiohu- 

 num rotundum and Opilio hystrix ; at the same time they are 

 strongly coiled together, somewhat in the same way as the 

 blood-vessel in the glomerules of the kidneys of Vertebrata. 

 Opilio hystrix^ the largest of the indigenous species in our 



* In Opilio hystrix ouly tlie uecli of the sacs shows a blackish or reddish- 

 brovvu tiiige. 



