8 Elementary Manual of Zoology. 
The Acanthocephala are parasitic worms armed with 
a protrusile proboscis furnished with hooks. They chiefly 
inbabit the digestive traets of Vertebrate animals, some- 
times passing through a stage of their existence in the 
grubs of insects (¢.g., eockchafers) upon which their ulti. 
mate host feeds. : 
(e) Annelida.—These are worms which have their bodies divided 
internally into well-marked segments and are provid d 
with definite blood-vessels. They comprise a number of 
groups of both sea and land worms, but the only ones that 
need here be noticed are the earth-worms and leeches 
which the students will be able to examine for themselves. 
Farth-worms are of great importance as soil-changers, for 
they are continually bringing up soil from below and 
depositing it above ground. Leeches, some of which are 
common forest pests in India, pass their early stages 
amongst vegetation or in water, where they are said to feed 
upon molluscs and other small animals, It is only in 
their later stages of growth that they affix themselves to 
mammals and fill themselves with warm bleod. 
(¢@) Rotatoria.—These are imperfectly segmented worms without 
definite blood-vessels. ‘I'he commonest representative is 
the little transparent wheel animalcule to be found in 
stagnant pools about Dehra. It may be recognised by 
the curious ciliated spparatus in front of the mouth, 
which serves to capture food particles in the water. 
(8) —Mo..usca. 
The Mollusca comprise all such animals as snails, slugs; oysters and 
cuttlefish, They are bilaterally symmetrieal, unsegmeuted, ecelomate 
avimals, with peculiar ventral foot and in many cases a caleareous shell. 
For an account of the structure of a typical representative of the Mollusca, 
see the chapter on the dissection of thesnail. The most important groups 
are the Lamellibranchiata, the Gastropoda, and the Cephalopoda. 
(ay Lamellibranchiata—These- are Molluses which have no 
distinct head differentiated from the rest of the body. 
They bave a bilobed fold of integument (mantle), which 
secretes a bivalve shell, They include a yast number of 
water creatures, such as oysters and mussels, but are of no 
very great importance from a forester’s point of view. 
The students should examine the bivalve shells in the 
Museum and sketch one or two typical specimens, 
(4) Gastropoda.—These are Molluscs with a distinct head which 
sometimes bears tentacles but never arms. They have an 
