360 fiXPLANATION OF THE PLATES. 



PLATE FOURTH. 



Fi(i. I. A male human tricocephalus, represented of the natural 

 size, in which the posterior part of the worm is seen to be 

 turned in a spiral manner. 



Fig. II. The female human tricocephalus, folded in its natural 

 size. 



Fig. III. The male tricocephalus, enlarged by the microscope 

 (no. 4, tube A.) — a,.The head whicli becomes insensibly round. 

 —a b c d ef, Course of the intestinal tube. — g /«, Transverse 

 lines made in form of ciowded rings. — /.:, Intestinal tube. — ■ 

 Im, A cylindrical body, surrounded by a very thin canula, 

 from which it is thrust out by mere pi-essure. May it not be 

 a principal part of the male ? In fact in all these viscera 

 there is not found the smallest trace of eggs or embrios. 



Fig. IV. The posterior extremity of the female tricocephalus, 

 (fig. II,) cut off at the commencement of the transverse rings, 

 and seen with the microscope (no. 4, tube A.) — a, The ex- 

 tremity of the tail quite obtuse, and different from that of the 

 male. — b c, The vermicular intestine twined round. In fe- 

 males it is quite filled with eggs; and de shows its course 

 winding round the intestinal tube, extending from / to the 

 aperture 5'. 



Fig. V. a b. Two eggs of the human female tricocephalus, ob- 

 served through the microscope (no. 2, tube A.) In a contort- 

 ed sack several hundreds have been found. 



Fig. VI. A tricocephalus of the lacerta apoda, as it is represent- 

 ed and described by Pallas. — a, The head, or anterior extrem- 

 ity, having a small button or knob. — b, The posterior extrem- 

 ity, or tail with double crotchets. — c. The scaly twisted part 

 near the posterior extremity. — A, The head, mouth and 

 crown, with the crotchets magnified by the microscope. 



Fig. Vil. The human ascaris vermicularis of the natural size. 

 — ff, The head. — &j The tail. 



Fig. VIIl. The iinale ascaris vermicularis, observed with the mi- 

 croscope (no. 4, tube A.)— .7, The head, having two lateral 

 oval eminences b c, separated in the middle by the mouth a.-^ 



