136 
PRESIDENTS ADDRESS. 
most important functions is probably to prevent the larvae of other 
animals from fixing on the surface of the colony. The life of the 
Polyzoa is absolutely dependent on a free access of water containing 
the minute organisms on which they feed to the mouths of the 
active individuals of the colony. Encrusting species belonging to 
their own class, or to Sponges, Tunicates, and other animals, are 
thus dangerous foes, and they are ready enough to take advantage 
of any opportunity of growing over a Polyzoon of suitable form. 
This overgrowth is, however, certainly not marked in the living 
parts of the colony ; and it appears to me highly probable that the 
avicularia help to prevent it by destroying or disturbing those larvae 
of encrusting animals which attempt to fix in their neighbourhood. 
The necessity for maintaining an unobstructed flow of water 
makes most Polyzoa intolerant of mud, but it is worth noticing 
that there are a few species which have succeeded in adapting 
themselves to the muddy conditions found in many parts of our 
East Coast and elsewhere. Of these I may specially mention 
Anguinella palmata, which, although accounted a rarity, occurs in 
great profusion between tide-marks at Dovercourt. A few other 
species such as Vesicularia spinosa, Alcyonidium yelatinosum, and 
others, are common in the muddy estuaries of the Suffolk coast. 
I have attempted this evening to give a few instances to show 
that the study of our Invertebrate fauna is one which is full of 
interest ; not merely from the point of view of recording species, 
but also in ascertaining the details of their life-history, the foes 
they have to contend with, and the utility of their several parts. 
Many of the most important advances in our knowledge of 
Invertebrates have been made by the careful observation of the 
living animals ; and as instances of this I have cited some of the 
observations of J. V. Thompson, Sir J. G. Dalyell, and others. 
Put much remains to be done in this field. The study of the life- 
histories of Insects is a pursuit in which great advances have yet 
to be made. The works of Professor Miall,* on Aquatic Insects 
* ‘The Natural History of Aquatic Insects,’ 1895; and ‘The Structure 
and Life-History of the Harlequin Fly ( Chironomus ) ’ (Miall & Hammond), 
1900. 
