INTERNAL ANATOMY OF THE GAMASIN.E. 291 



the two species, both are developments of the ring system upon which the genitalia of 

 both sexes in the Acarina, and, indeed, in other groups of the Arachnida, are so 

 frequently based; but this is not saying much, for the varieties which nature gives us in 

 this ring are so numerous and so diverse that they would scarcely seem greater if based 

 upon a separate plan. 



Winkler mentions that the distal portion of the ductus ejaculatorius is coated with 

 chitin. In G. terribilis this chitinous coating rather assumes the form of a short 

 chitinous trough, not entirely surrounding the mouth of the ductus, but in which the 

 latter lies ; while a partial chitinous ring, like one of those, in a pseudo-trachea of the 

 blow-fly's tongue, is fouud within the mouth of the tube; the reason for this difference 

 may possibly be the size of the bodies that have to pass through the ductus ejaculatorius 

 of G. terribilis. 



It may be as well to say a few words as to the maturation of the sperm-elements in 

 this testis, particularly as it affects later portions of this paper. 



In the attenuated end of each testis, from the part where it joins its fellow of the 

 opposite side for a short distance onward, we find, inside the tunica propria, &c, which 

 covers the whole organ, a closely-packed quantity of cells, which at the narrowest part 

 are extremely small and gradually increase in size ; but iu each cell, wherever it is 

 amenable to the microscope, we see the nucleus quite clear and distinct ; although in 

 the smaller cells it is scarcely possible to see a nucleolus. As we examine the testis, 

 proceeding toward the ductus ejaculatorius, the cells gradually and steadily increase in 

 size, until we arrive nearly at the point where what I have spoken of as the more 

 perpendicular portion joins the horizontal part. Near this point the cells, which w r e 

 may call " sperm-mother-cells," have attained a remarkable size, some of them measure 

 as much as 170^x125^; each cell still retains a large clear nucleus, which in a cell of 

 the above measurement would be about 58 ft and would possess a w r ell-marked nucleolus 

 of about 25 p. Before the mother-cell had attained this size a number of minute, nearly 

 globular bodies, clear but highly refractive, and not at first measuring more than 1 ,<i to 

 2)t, will have formed in contact with the inner side of the peripheral protoplasm ; these 

 I consider to be the true spermatozoa in an early stage. When the cell has attained its 

 full size the interior of the peripheral protoplasm is nearly coated with them ; the cell, 

 however, still remains fairly transparent, or at least translucent. The nucleolus has 

 already shown signs of breaking up. 



On passing from the perpendicular to the horizontal part of the testis a great change 

 takes place in the sperm-mother-cell, its nucleus breaks up entirely, or sinks into the 

 centre of the cell ; the spermatozoa break off from the peripheral protoplasm and collect 

 in a mass in the middle of the cell ; this mass is closely agglomerated and no longer 

 transparent, and a clear space is left between it and the peripheral protoplasm ; the whole 

 cell now presents the appearance of a partially-filled spermatocyst. The spermatozoa 

 continue to increase slightly in size, until in the ripe cells nearest to the vasa deferentia 

 they may measure 3 n to 1 p ; the sperm-mother-cell itself has, however, shrunk a little, 

 and in a testis where the largest mother-cells were of the above measurement those fully 

 ripe would not exceed about 135 p X 89 /.i . These measurements are taken all through from 



13* 



