SKELETO-TROPHIC TISSUES AND COXAL GLANDS. 161 



him to give to them the name of " the brick-red glands." 

 This colour they lose when placed in alcohol. If a section of 

 the gland is examined in the fresh state, it is found that the 

 red colour is due to the presence of numerous small red- 

 coloured granules which occur in the layer of gland-epithelium. 

 A piece of this epithelium, as seen in the fresh state without the 

 addition of any reagent, under a No. 10 immersion of Hartnack, 

 is shown in Plate XI, fig. 6. The red granules are there pre- 

 sented with their natural colour. In this fresh condition the 

 nuclei of the gland- cells are not seen, owing to the refractive 

 properties of the living tissue. 



12. General conclusions as to the coxal glands of 

 Scorpio, Mygale, and Limulus. 



The minute structure of the glands above recorded leaves 

 little room for doubt that we have in the coxal glands an active 

 secretory apparatus. The materials upon which the gland- 

 epithelium acts are probably brought to it by the intermediary 

 of the intercaecal tissue, and the product of secretion is accu- 

 mulated in the lumen of the gland-caeca. But it must be 

 admitted that no abundant or peculiar-looking secretion can be 

 detected in this lumen — only in some cases a colourless coagu- 

 lable material — and further, it seems that there is no outlet for 

 this secretion. 



On the whole, the facts seem to favour a comparison with 

 the green-glands (antennary coxal glands) of the Decapod 

 Crustacea. But these glands have a definite outlet, and also 

 show a difi'erent structure in their gland epithelial cells, as 

 seen in the portion of the green gland of Palsemon, figured 

 in PL VIII, fig. 8. These latter have no trace of the fibrillated 

 cortical substance which characterises the gland-cells of the 

 coxal glands equally in Scorpio, Mygale, and Limulus. 



It seems to me that, until we have embryological evidence to 

 the contrary, we must still hold the possibility before our 

 minds of the development of these coxal glands of Arachnida 

 from skeleto-trophic tissue. They may be, from beginning to 

 end, a product of the diflferentiation of such tissue, like some 



VOL. XXIV. NEW SER. L 



