Gall-producing Anguillulide. 345 
living in plants are oviparous*, and that they have their genital 
apertures in the vicinity of the posterior extremity of the hae 
This is precisely the case in the Anguillula of the milfoil ; 
is Oviparous, and the genital apertures of both sexes are more 
or less near the caudal extremity. ‘Their distance from the 
latter must be regarded, in the present state of our knowledge 
of these animals, a as one of the best of the few specific characters. 
The male has a somewhat curved linguliform penis, rapidly 
attenuated from a broad base; this can be pushed forth from 
the anus, which surrounds it like a sheath, and opens obliquely 
backwards and outwards. The cleft-like anal orifice, which 1s 
placed transversely to the longitudinal axis of the body, has a 
slightly prominent margin, and is situated at a distance of 
one sixteenth or one seventeenth of the total length of the 
body from the end of the tail. Immediately behind the anus 
the transverse diameter of the body of the male diminishes 
considerably ; it tapers off quickly to a point, which in the 
adult male is always bent almost angularly in a direction 
away from the anal aperture. In most cases the penis was 
retracted within the anus, so that the margins of the latter 
closed together; only in one individual did the apex of the 
pea project from the anal cleft, when it was distinctly seen 
to be a little broader than thick, i. e. tongue-shaped. The 
magnifying-power with which I worked did not enable me 
to see distinctly the two spreula and accessory parts, of which 
the penis of the Anguillulidee consists. 
A short distance in front of the male genital aperture, about 
the beginning of the last twelfth of the “body, there originates 
a very delicate, perfectly transparent membrane, which extends 
over the above-mentioned genitalia to the hinder extremity, 
and is attached to the sides of the body. This membrane is 
usually tightly stretched, only appearing slightly folded trans- 
versely in dried individuals. When the male is laid exactly on 
his back, the membrane described is frequently seen to project 
a little laterally beyond the margin of the body; but in most 
instances this is not the case. 
* As Linné was already aware (see note §, p. 843), the Anguillulide 
are » gang gma oviparous, sometimes viviparous. These different. modes 
of reproduction even occur in the same species ; for Goeze reports 
(“ Mikrosk. Erfahrungen iiber die Essigaale,’”’ in the ‘ Naturforscher,’ 
Stiick i. 1774, p. 34) that the Anouillules of vinegar bear living young 
after the manner of the Aphides, from July until autumn, and in the 
autumn lay eggs which survive the winter. Nay, even the same indi- 
vidual may be both oviparous and Viviparous ; for Claus states (Zeitschr. 
fiir wiss. Zool. Bd. xii. 1865, p. 354) that his oviparous 4. brevispinu is 
identical with Grube’s A. mucronata, as in this species the same female 
produces her first brood oviparously and the later ones viviparously. 
