682 THE ANIMAL KINGDOM. 



least developed form it consists of a slight cuticular ridge on either side of 

 the tail, which begins anteriorly to the anus. The ridges may become thin 

 folds, which may or may not be connected in front of the anus, and some- 

 times stop short of the apex of the tail, or extend beyond it. These mem- 

 branes are best developed in Strongylus^ where they form an umbrella-like 

 expansion. The ventral area inclosed by the bursa is provided with 

 sensory papillae, sometimes with ridges, spines, a sucker, as in the genus 

 HeterakiS) or five suckers (?) on either side the anus, as in Nematoxys 

 ornatus 1 . 



The female aperture is usually on the ventral aspect and near the 

 middle of the body, but it may be close to the mouth, or just in front of 

 the anus, as in some Strongyli. It is generally a cross slit with more or less 

 prominent margins, and in Trichocephalus is supported by a spinulose 

 papilla. The female sexual tube is divisible into vagina, uterus, oviduct (or 

 tuba), and ovary. The vagina is always short, and in small Nematoda 

 scarcely visible. It is an invagination of the cuticle and subcuticula. The 

 remainder of the tube has a wall composed of a delicate membrane lined by 

 an epithelium which has a characteristic shape in its different sections. In 

 the uterus and lower part of the oviduct it consists of polyhedric plates, 

 usually numerous, bearing papilliform projections, and separated by furrows. 

 The papillae probably secrete a substance which cements the ova together 

 while the furrows give shelter to the sperm. The epithelium of the ovary 

 consists of nucleated protoplasmic bands ; that of the upper part of the 

 oviduct is a nucleated protoplasmic layer in A. megalocephala. The lower 

 part of the oviduct and the uterus have an external muscular layer of 

 chiefly transverse fibres, whilst the vagina has fibres which radiate towards 

 the lateral areae. The genital tube is of greatest length in the larger 

 Nematoda, in which it is disposed in many longitudinal coils ; it is short 

 and simple in the smaller species. It may be single and directly prolonged 

 from the vagina as in Trichina, &c. ; double, and then one branch may run 

 towards the head, the other towards the tail, the vagina being at right 

 angles, e. g. Oxyuris, Strongylus, &c. ; or the two branches may run either 

 parallel or at an acute angle to one another. A greater number of branches 

 than two is rare. The spermatozoa accumulate near the junction of the 

 uterus and oviduct ; hence this part is sometimes termed spermatheca. 

 They become mixed with the descending ova, and those which do not effect 

 impregnation appear to reascend to the spot named by means of the intra- 

 epithelial furrows. 



Remarkable peculiarities are the following: In the impregnated female 

 Sphaerularia which inhabits the cdelome of the Humble Bee, the uterus 

 undergoes prolapsus, and while the body of the Worm is only ^V m - 

 long, the prolapsed uterus with the contained genitalia and a loop of 



1 See Schneider, Die Nematoden, p. 113, sub sp. 



