I 



OP THE NEMATOIDS, PARASITIC AND PREE. 605 



their typical condition in the Anguillulidce. We find in the female a transverse vulva 

 opening near the middle of the body in the ventral region, with a short vagina leading 

 into a symmetrical, double uterus whose cornua extend on either side ; these uteri are 

 separated by constricted portions from narrower oviducts, whilst these in turn commu- 

 nicate with reflexed ovarian tubes. The oviduct has scarcely ever a greater proportional 

 length than is represented in the figure, and is often proportionally much wider, as 

 may be seen in the members of the genus Plectus (Plate XXVIII. fig. 15). We never 

 meet with the long filiform ovaries so characteristic of many of the parasitic Nema- 

 toids. In a certain number of the Anguillulidce, however, the vulva is situated near 

 the commencement of the posterior third of the body, as in the genera Monhystera, 

 Tylenchu^, &c., and in these cases the posterior uterine segment remains undeveloped, 

 whilst the anterior half which does exist preserves the characters above described. In 

 the male there are two somewhat elongated ovoid sacs or testicles, connected by narrow 

 canals with the commencement of a simple tube or vas deferens, which opens externally, 

 together with the intestine, at the anal cleft. On either side of its termination, and 

 capable of being protruded through the anal cleft, are two spicules, equal in size and of 

 a horny nature. These spicules may be either solitary, or provided with one, two, or 

 even four accessory pieces. In two species, Monhystera ambigua and M. disjuncta, I 

 have seen the genital tube opening separately from, and anterior to the anus. In the 

 fonner I was also unable to detect spicules of any kind, whilst in the latter, curiously 

 enough, they were in their usual situation, and therefore quite separate from the ter- 

 mination of the genital duct*. In certain genera, such as Rhabditis and Monhystera^ 

 the male genital tube appears to be connected vrith only one testicle, which is separated 

 by a constriction from the efferent ductf . 



The spicules amongst the free Nematoids are not enclosed in a distinct sheath, such as 

 we find amongst the Ascarides and many other parasitic Nematoids. In the genus 

 Ascaris two equal spicules, each enclosed in a firm thick-walled sheath, are generally met 

 with, one on each side of the body (Plate XXV. fig. 7 n, 6), but in Ascaris lumbricoides 

 I have found them very unequal in size and situated close to one another (Plate XXIII. 

 fig. 4). 



The structure of the genital organs met with in the Guineaworm is, so far as I have 

 seen, quite unique amongst the Nematoids, though it seems more easy to connect it with 

 an extreme modification of organs such as are met with amongst the free Nematoids, than 

 with anything similar amongst others of the parasitic species. The histological differ- 

 entiation of its tissues, and the developement in it of well-marked elastic tissue, similar 

 to what is met with in the vascular system of higher animals, is an interesting factj. 



The spermatozoa in the parasitic Nematoids, so far as we know at present, are generally 



* See, for this and various modifications in the form of spicules, " Monograph on Anguillulida3," Trans, 

 of Linn. See. pis. 9-13. 



t Well represented by Davaiite in E«cherches sur rAng:uillule du ble nielle, pi. 3. fig. 1. 

 t Trans, of Linn. Soc. vol. xxiv. p. 118, pi. 22, figs. 34 & 37. 



