Aims and objectives

This exercise is designed to demonstrate:

1. How earthworms respond to not-self matter entering their body cavity, including parasites.

2. How to generate quantitative data for subsequent interpretation by summary statistics, graphs and statistical analysis.

Introduction

All living cells need to be able to distinguish self from not-self molecules. This ability is necessary for activities as diverse as feeding (by phagocytosis/pinocytosis), fertilisation and building multicellular bodies. The more complex an animal becomes the more the integrity of its body is threatened by the invasion of infectious organisms and by the appearance of mutant cells (‘cancers’). Self and not-self recognition as a form of adaptive response is seen in all metazoa, the process becoming increasingly more complex in the higher invertebrates, and qualitatively more sophisticated, with the evolution of the immune response, in the vertebrates.

This practical will examine aspects of the ability of a common invertebrate, the earthworm, to recognise not-self molecules. Earthworms have a body cavity, the coelom, and a well-developed blood system. The fluid in the coelom contains free cells, amoebocytes, which carry out a major part of the self/not-self recognition. Amoebocytes can phagocytose material as well as encapsulate objects that are too large to ingest. Aggregations of amoebocytes around foreign bodies form the large ‘brown bodies’ that accumulate in the tail-end of the coelom.