A NEW SPECIES OF PENTASTOMUM. 185 



contrast in appearance, and has no such lining, it would seem justifiable to 

 assume that the point where these two come into relation with each other is 

 also the point where what may be termed the inward and outward growing 

 portions of the generative apparatus meet, Furthermore, the immaturity of 

 the specimens before us, indicated by their encysted condition, is in support of 

 this, for it is quite conceivable that, as sexual maturity approaches, a connec- 

 tion might be formed between these two canals. It is to be noted, however, 

 that in Leuckart's figures of the sexual organs of L. tamioides, the channel is 

 shown as quite pervious from the exterior to the testis even in so early a stage 

 as that known as P. denticulatum* which measures only 4'5-5 mm. in length ; 

 but in describing the stage immediately preceding, which has a length of 

 3 mm., he mentions that the communication with the cirrus sac and the hinder 

 portion was not clearly observed (" Eine Communication mit den dahinter 

 gelegenenen Leitungsapparaten wurde mit Bestimmtheit nicht beobachtet").t 

 If this explanation be the correct one, it is curious that the species before us 

 should present such a striking embryonic feature when the remainder of its 

 organisation has attained such a comparatively advanced stage of development. 



4. The Cirrus Sac is shown in longitudinal section in PL XXVIII. fig. 10, 

 and may be seen to be roughly divisible into two portions, — a solid part through 

 which the vas deferens passes, situated on the dorso-lateral aspect, and a 

 hollow part placed nearer to the ventral line. The latter portion is, speaking 

 roughly, ovoid in form and slightly flattened in the radial direction of the 

 animal's body, as seen in the section (fig. 11): anteriorly it gives off a tube 

 from either side (fig. 10). One of these is the ejaculatory duct, the position of 

 whose aperture near the middle line of the body has been already described ; 

 its lumen becomes gradually smaller until it reaches 0005 mm. 



The other tube-duct of what seems to be a gland, which, under the name of 

 accessory, will be presently described. 



The wall of this saccular portion is on the average about 0*036 mm. in 

 thickness ; its innermost layer is of chitin so thin that it appears only as a fine 

 though very distinct line under a power of 400 diameters ; next follows an 

 epithelial layer, 0-008 mm. in thickness, of nucleated columnar cells; the 

 remainder of the wall being composed of small cells among which run a number 

 of muscular fibres, these last being confined to the anterior portion of it. 



The solid portion of the cirrus sac is an ovoid mass somewhat smaller than 

 the other part, the wall of which covers it to a certain extent, though even- 

 tually it fuses with it. Through the middle of this mass of cells passes the canal 

 of the vas deferens, slightly widening as it approaches the sac until it ends in a 

 short groove (PI. XXVIII. fig. 10 ; also in section fig. 11, v.d). 



A short distance posterior to this is another orifice leading into a cavity 



* Loc. cit., Tab. iv. fig. 11. f Loc. cit., p. 134. 



