THE ANATOMY OP PENTASTOMUM TERETIUSOULUM. 45 



spermathecse are large prominent structures, just as described 

 by Leuckart, Hoyle, &c. They are filled with a dense mass of 

 mature spermatozoa (fig. 22). Their walls are, save where 

 the duct passes out, of uniform thickness, and formed of a very 

 distinct single layer of cylindrical epithelium cells (•! mm. in 

 length), on the inner surface of which is a fine cuticular layer, 

 whilst their outer ends are embedded in a finely granular 

 material, the whole being covered externally by a layer of 

 muscle-fibres (fig. 55). The function of the latter must be, as 

 stated by Leuckart, that of lessening by their contraction the 

 size of the organ, and of thus driving out some of the contained 

 spermatozoa. The cylindrical epithelial cells are very sharply 

 outlined ; their inner ends are granular and packed closely 

 together ; their median portions are comparatively free from 

 granules, and each one contains a distinct oval nucleus. Their 

 outer ends are somewhat tapering, spaces being thus left be- 

 tween them, and they are embedded in a granular substance. 

 Leuckart has naturally suggested that they may secrete a 

 material which serves to preserve and nourish the sperm, but 

 in no instance could I detect any trace of the remains of such 

 a material, or any indication of its passage from the cells into 

 the cavity. The presence of the thin cuticular lining, which 

 shows no break or trace of pores, is also against the idea of 

 these cells being secretory in function ; though, on the other 

 hand, the peculiar and uniformly granular appearance of their 

 inner ends certainly gives rise to the idea that they are 

 elaborating material of some special nature, probably the 

 chitiuous lining. 



The ducts of the spermathecae are of a very special and 

 peculiar structure. Each has the form of a short tube running 

 in a curved direction from the spermatheca of its side to the 

 median line, where the two unite together on the ventral side 

 of the common termination of the oviducts. The concavity of 

 the curve faces posteriorly (fig. 41). They are lined internally 

 by a layer of nucleated columnar cells thrown into folds, and 

 very similar to those of the vagina (fig. 54, Sp. D. E.) Their 

 internal ends sometimes appear to have a very thin cuticular 



