ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 639 



5. Arachnida. 



New Hypothesis as to the Relationship of the Lung-book of 

 Scorpio to the Gill-book of Limulus.* — Prof. E. Eay Lankester with- 

 draws his suggestion that by the enlargement of the hollow stigmata 

 connected with the thoracobranchial muscles of an ancestral scorpion 

 the branchigerous appendage might come to lie in the pit of the 

 tendon of the muscle, and that eventually the hollow might inclose 

 it, and replaces it by a more simple explanation. He was led to give 

 up his earlier view by finding that the veno-pericardiac muscle 

 attached to the apex of each lung-sinus in Scorpio had no relation to 

 the thoraco-branchial muscles of Limulus, but was represented in it 

 by exactly similar veno-pericardiac muscles. 



In Limulus, as in Scorpio, there is on each side of the sternal 

 surface a great blood-sinus in free communication with the lamelli- 

 gerous organs. If we suppose the mesosomatic appendages in the 

 Scorpion branch of the family to grow relatively smaller and smaller, 

 and to be purely respiratory in function, and to be aerial rather than 

 aquatic ; we have only further to imagine the four hinder pairs to 

 have taken on in the embryonic condition a very common trick of 

 growth, viz. an inward growth of invagination, to have the exact 

 condition of the modern scorpion's lung-book. 



The best known example of such inward growth is seen in the 

 hydatid-stage of Tcenia solium, and the introversion is probably due 

 to external pressure. Now, it is to be borne in mind that in the 

 modern scorpion development goes on within the ovary ; the pressure 

 of the ovarian tunic must be considerable, and is at any rate a 

 possible cause of the invagination. 



Coxal Glands of Mygale.f — Dr. P. Pelseneer describes the coxal 

 glands in a large South American Mygale (Theraphosa). The two 

 glands, which are quite separate, are placed on each side of the cepha- 

 lothorax, at the side of the entosternite (enthodere of Duges) between 

 the lower plate and the upward prolongations of it, to which latter 

 they are intimately related in position, size, and form. 



As surmised by Prof. Lankester, this gland is not a simple ovoid 

 glandular body, as in Scorpio, but is furnished with lobes correspond- 

 ing to the coxae of the cephalothoracic appendages, as in Limulus. In 

 addition to these four coxal prolongations, the gland has two internal 

 projections near its middle third, corresponding to two slight excava- 

 tions of the entosternite, between its lower plate and its upper pro- 

 longations. The colour of the gland is uniform, a brownish-yellow, 

 not unlike that of tho stomach and its lateral diverticula. Its 

 appearance is coarsely cellular, showing distinctly the groups of colls 

 of which it is made up. No efferent duct, either passing to the 

 exterior, or to any internal organ, was seen. Tho gland in Mygale, 

 like that of the adult Limulus and Scorpio, is therefore a closed 

 gland. 



• Quart. Journ. Micr. Sci., xxv. (188r>) pp. .3.30-42. 

 t Proc. Zool. Hoc. Lond., ISS."), pp. JJ-U (1 pi.). 



