Chloragogen cells of earthworm are analogous to liver of vertebrates.

Trochophore is cilliated, larval stage of polychaetes, molluscs and rotifers. Neopliliva, chiton and Pila belongs to Phylum- Mollusca. Molluscan development is either direct or with metamorphosis through the trochosphore stage.

A typical vertebra has a centrum or body and nerval arch. The hole formed by the neural arch is the vertebral foramen. The vertebral formaina of all vertebrae form the vertebral canal or neural canal.

Radius and ulva are the bones of the fore-arm. Which are closely held together. The ulna is the long bone and bear a deep sigmoid notch for articulation with the trochlea of the humerus.

Digestion is a process in which non-diffusible foods are converted into diffusible foods with the help of digestive enzymes. It is mostly carried out by the process of hydrolysis using water molecules for the cleavage. The enzymes which bring about digestion are called hydrolases.

Chordate animals at some time in their life history exhibit the following three diagnostic characters

(1) Presence of notocnord.

(2) Presence of dorsal tubular nerve cord.

(3) Presence of gill clifts during development

Beside these some other characters are :

(a) ventral heart

(b) Hepatic portal system.

The chief functions of the large intestine are the absorption of water and the elimination of solid wastes. Large intestine in divided into three parts, i.e.caecum, colon and rectum.

In mammals, colon has essential water absorbing role in preparation of faeces.

Main characteristics of Class- Crustacea and Insects are as follows:-

1. Class Crustaces: They are mostly aquatic with gills, two pairs of antennal and three pairs of jaws, appendages. These are mostly biramous and always more than four in the trunk region. Eg, Prawn, Crab etc.
2. Class- Insecta : These are hexapod arthropods with a pair of antennae and three pairs of jaws. Eg, Cockroach, Grasshopper etc.

Urea formation takes place in liver through ornithine cycle. The blood leaving liver and going towards heart has high amount of urea.

Food storage in Leucosolenia occur by thesocyte. Thesocytes have lobore pseudopodia and are filled with food reserves, thus acting as storage cells.