Did 

Some threadworms are found in plants, such acid liquids, feeding on the small fungi which are 
as Anguillula tritici, a microscopic species which | there produced. It is just visible to the naked eye, 
infests wheet. A nearly allied non-parasitic form is | but now that vinegar is more carefully manufactured, 
Anguillula aceti, the Vinegar Eel, which is found in | it is much less frequently observed than formerly. 
Order Il. Acanthocephali. 
These are tube-like worms withovt mouth or | vertebrate animals, and develops itself if its host is 
intestine, but with a retractile proboscis bearing hooks, | eaten by a higher animal. They very rarely infest 
with which the fully-developedanimalsattachthemselves man; one species, Lchinorrhynchus gigas (fis. 
to the wall of the intestine in vertebrate animals. ‘th 
The asexual larval form encysts itself in small in- 
45 a 
Sy 1S 
found in the pig, and its embryo form in the grub 
of the Cockchafer, 

Class ¥. Plathelminthia. 
This is a large division, including the lowest | an excretory duct, but may be altogether absent. 
worms, and derives its name from the flattened form | Most species are hermaphrodite, and they undergo a 
of the unsegmented body. Only the higher species | complicated series of metamorphoses, often combined 
possess blood-vessels and respiratory organs, and the | with alternation of generations. Some are parasites, 
digestive system is not only able to dispense with | but many live in mud and under stones in the water. 
Order |. Turbellaria. 
These are worms of an oval or ribbon-like form, | tenacious of life, and are gifted with great powers 
with the surface of the body uniformly clothed with | of reproduction. 
minute cilia. They are not parasitic, and have no The Flanarie are of smaller size, and usually 
grasping or sucking organs. Their development is | of oval form; many species inhabit fresh water; 
frequently direct. among which is Flanarza alba (fig. t). This and 
The Nemertina occupy the highest place, from | other species (generally black or brown) are found 
their large size, more complicated structure, and the | about stones and rushes in brooks, ponds and marshes. 
separation of their sexes. Only one small form is | In spring they deposit small round or oval capsules 
found in fresh water. Most of the species are marine, | of the size of a pin’s head, and often stalked, con- 
and often finely coloured. They are distinguished | taining 4 or 5 delicate eggs. Among the marine 
by possessing an extensile proboscis, which is armed | species, the eggs are often laid in strings. As may 
in many species with a dagger-like weapon, used to | be seen in the transparent Flavari@, the intestine 
impale other and smaller organisms. Portions of | is branching, a character common to all the Zwr- 
their body are easily lost, but they are extremely | deMarza. 

Order I]. Trematoda. 
These animals differ from the last in their para- | numbers of the animals. It passes its early stages in 
sitic habits. They have no body-cavity, but the | fresh-water snails, and therefore chiefly infestssheep 
organs are embedded in a matrix of uniform con- | which feed in swampy situations. 
sistence. They possess organs of suction, the num- On the other hand, all the Zrvematoda with 
ber of which serves to characterise the different groups. | more than two suckers have a direct development, 
Fig. u. Fasciola hepatica, the Liver Fluke, | without metamorphoses. 
is one of the commonest and most dangerous para- Fig. v. Tristomum coccineum represents a 
sites. It lives in the gall-ducts of the sheep, sucks | genus of parasites which infest the skin and gills of 

the juices of the liver, and frequently destroys large | fishes. 
Order Ill. Cestoda. 
The tapeworms close the series of worms, and | their development, fix themselves everywhere, and 
hideous as they are, their life-history is of much | if swallowed, make their. way into the blood-vessels, 
interest and importance. The fully-developed sexual | and are thus carried into the liver, lungs, muscles, 
animal has neither intestines, respiratory organs, nor | brain &c., where they assume a bladder-like form 
organs of sense. It has a ribbon-like form, and | containing fluid (Cysticercus). As in the Trichine 
consists of a number of joints (proglottides) increas- | these sexless forms gradually perish, unless the flesh 
ing in thickness and breadth hindwards. It fixes | in which they are embedded is eaten, when they 
itself with its head to the wall of the intestine of | assume the form of a tapeworm in the intestines of 
some vertebrate animal, and the whole chain hangs | their new host. It follows from this that the two 
loose in the intestine. Every separate joint is fur- | forms must inhabit animals whch have a certain 
nished with sexual organs, and the last, which is | relationship to each other. Thus the Cysticercus 
always the most developed, becomes filled with eggs, | of the tapeworm of the cat is found in the mouse. 
drops off, and is discharged in the natural way. The | Although the tapeworm causes debility rather than 
minute embryos, which require another animal for | actual disease, the presence of Cystcerci in large 

