Class 1. Nematoda. 163 



Iwres into a Cyclops in which it undergoes cei-tain changes. In Man, infection is 

 probably the result of accidentally swallowing the Cyclops in di-inlring water. 



(b) Pilaria immitis (fema-le to 25, male to 17 c/m), in the heart and hypo- 

 dermal connective tissue of the Dog ; the young forms in the blood. Common in 

 Eastern Asia, rare in Europe. In the tropics the young Filarix are also found 

 in the blood of Man. 



7. Mermie. Filiform aproctous Round-worms inhabiting various Insects, 

 out of which they finally bore into damp earth, where they become sexually 

 mature, copulate, and lay their eggs. The lai-vse bore their way again into the 

 tissues of Insects. The genus Gordius, far removed in structure from the 

 typical Nematoda, and living, in the adult state, in fresh water, presents a 

 similar, but more complex, life-history. 



8. The Anguillidie are a group of Ifematodes, which are, for the most part, 

 veiy small, and usually free-living, occurring in water, in different decaying 

 substances, or in living plants. As examples, the following may be mentioned : 



(a) Tylenchus tritici, the Eel-worm. In grains of wheat there is sometimes 

 fotmd a fibrous mass, which, upon closer examination, proves to be a. number 

 of small dried-up Nematodes ; they are restored to 

 animation by moistening. When such " ergots " are 

 sown with sound grains, the Nematodes leave them and 

 mount the growing wheat plants, upon which they may be 

 met with between the glumes; later they bore into the 

 grains, in which they become mature and lay their eggs. 

 The young ones hatch from these and are found in the 

 ergots arising by modification of the grains. 



(6) Seterodera schachtii, another Eel-worm, produces 

 the so-called root-knot. The larva bores into the delicate 

 roots of the beet (and various other plants), and attains 

 maturity there. The ripe female, which is distinguished by pj -|^.,j jjetero- 



its short, citron-shaped form, pushes the hinder end of its dera Schachtii. 

 body out from the root, causing the epidermis of the root Female fastened to a 

 to split. The elongate male, on the other hand, bores root-fibre. Enlarged, 

 entirely out, and seeks the female for fertilization. The ^' 



impregnated female later (Fig. 125), by the degeneration of 

 the organs,becomes a brood pouch full of ova and larvae, and finally drops off the root. 



(c) Anguillula aceti, the Yinegar worm, lives in sour paste and in vinegar. 



Class 2. Acanthocephala {Tkom-headed Worms). 



The body is cylindrical, elongate, often transversely wrinkled, and 

 fairly hard. There is an eversible process, the so-called proboscis, 

 at the anterior end^ which is beset with many rows of backwardly 

 directed chitinous hooks ; the rest of the body is usually .smooth. 

 In the skin there is a peculiar vascular net-work, continued 

 into two long bodies (the lemnisci), which spring from the body- 

 wall, in. the anterior region of the body-cavity. A digestive 

 tract is entirely wanting. Pood is absorbed through the 

 surface, and the vascular system and the lenmisci probably carry the 

 nutritive fluid from the skin over the rest of the body. The nervous 

 .system is represented by a ganglion lying in the forepart of the 

 body, at the base of the proboscis, from which nerves run backwards 

 and forwards. There are no sense organs. The Acanthocephala 



M 2 



