Miscellaneous. 389 



clusters of cells which become insensibly united with the surround- 

 ing connective tissue, without its being possible to say where the 

 glandular tissue commences and where the connective tissue ends. 

 It was on account of this arrangement that Hay Lankester, who, 

 moreover, was not aware of the communication between the medul- 

 lary and the cortical substance, and of the double lacunar system 

 constituted by the sanguineous and the glandular lacunae which I 

 have just described, regarded this medullary substance as being 

 formed by a connective tissue of a special kind, the nature of the 

 emjjty spaces of which remained problematical to him ; never- 

 theless his shrewdness led him verj- justly to consider this medullary 

 substance as probably corresponding to the sac of the antenuary 

 and shell-glands of the Crustacea. 



The structure of the cortical substance of the coxal gland of the 

 Scorpion is actually known. I shall therefore confine myself to 

 stating that the injections which I have made of it with celloidin 

 and asphalt have entirely confirmed the current opinion, which 

 I'egards this substance as being formed of an extremely long tube 

 coiled a very great number of times upon itself. The mould which 

 is obtained by this method gives a demonstration of this structure 

 which is conclusive in a very different way from that hitherto 

 derived by authors from the method of sections. This tube com- 

 municates by one of its extremities with the medullary substance, 

 and I may remind the reader that, as has recently been shown, it 

 opens to the exterior by the other at the level of the base of the 

 third pair of limbs. 



The secretion of the cortical substance is effected by elimination 

 of large vesicles at the extremity of the cells in a manner similar to 

 that ■n'liich we have described in the Crustaceans. The cells of the 

 medullary substance frequently present sharp constrictions, or a 

 biscuit-shape, which indicate a mode of secretion analogous to that 

 of the sac in many of the Decapods, 



Conclusion. — It follows from the foregoing that the antenuary and 

 shell-glands of the Crustaceans, as well as the coxal gland of the 

 Arachnids, may with reason be considered as organs of the same 

 nature. The morphological significance of the sac of the Crusta- 

 ceans is moreover found to be elucidated by the study of the medul- 

 lary substance of the coxal gland of the Scorpion ; and the opinion 

 of Lankester, who was led to consider the epithelium of the sac 

 as being formed by difi"erentiated connective tissue, its cavity being 

 a portion cut off from the ccelome, isolated and adapted to excre- 

 tion, thus receives entire confirmation : the glandular lacunae of 

 the medullary substance of the Scorpion may in fact be considered 

 as being excavated in the midst of a differentiated connective 

 tissue. 



The antenuary gland of the higher Crustaceans, the shell-gland 

 of the lower, and the coxal gland of the Arachnids, communicating, 

 as we have seen, on the one side with the exterior, on the other 

 with a cavity which may be considered as a derivative of the ca-lome, 

 may bo regaided with much probability as forming part of a meta- 



