Systematic Course. ad 
For an account of the structure of.a typical representative of the group, 
see the chapter on the dissection of the earthworm, Worms are divided 
into a large number of sections, but the following are the only ones s that 
the students need notice :— 
(2) Platyhelminthes.—These are flattened worms without true 
segmentation. They include a large number of very 
different animals, of which we may notice :— 
(1) The liver-flakes: which in their adult form are para- 
sitie in the bodies of sheep and other animals, 
while in their immature form they pass through 
a series of complicated transformations in the 
tissues of snails, etc. 
(2) Tape-worms, which in their adult condition are para- 
sitic in the digestive organs of mammals, while in 
their immature form they inhabit the tissues of 
animals of many different kinds which the even- 
tual host eats. They usually present a specialised 
form of spurious segmentation due to the multipli- 
cation of the posterior part of the body in which 
the reproductive organs are situated. 
(8) Free living sea forms, such as the gliding worms 
(Turbellaria), which are interesting as comprising 
some of the simplest organisms of the group. 
(6) Nemathelminthes.—These are round or thread-like unseg- 
mented worms, comprising a large number of forms para- 
sitic on animals and plants. The two most important 
groups are the Nematoda and the Acanthocephala. 
The Nematode worms include the parasitic round and 
pin worms common in the digestive tracts of mammals, the 
parasite (Dochmius)! which passes through one stage of its 
existence in the human digestive tract and another stage 
in the earth, minute Filaria, which often infest the blood 
of mammals and birds in India, and which have been 
supposed to pass through a stage of their existence in the 
mosquito, minute Trichinw, which make their way into the 
muscles of mammals, producing a disease known as Trichi- 
nosis, also thread-worms, which are parasitic on locusts and 
other insects, and numerous species which are parasitic on 
plants. Nematode worms for the students to examine are 
usually to be found in large numbers in the tissues of the 
Dehra fresh-water crab—vzde chapter on the dissection of 
this creature, 
1 Said to produce the so-called kala-azar and beri-beré diseases which have caused an 
enormous number of deaths of late years in Assam. 
