president’s address. 
121 
decaying remains of the Duckweed, the lower layers of which 
have a deep black colour and smell strongly of sulphuretted 
hydrogen. Mud of this character was found by Lauterborn to 
have a characteristic fauna, including the interesting Rhizopod 
Pelomyxa and numerous forms of Infusoria, and also a number of 
species of the little known group Gastrotricha, some of which 
were previously recorded from North America only. 
But although much yet remains to be done in the mere recording of 
the species of aquatic animals found in Norfolk, my main object 
to-night is to call your attention to the importance of studying 
their Natural History. The determination of the species to which 
an Invertebrate belongs /nay be a matter which can only satis- 
factorily be dealt with by a specialist. The study of Invertebrates 
sometimes suffers from the want of easily accessible monographs. 
The literature of the subject is spread over an immense number of 
scientific memoirs, published in various languages, and often not 
to be found except in the largest libraries. It must therefore be 
admitted that a naturalist who takes up the study of a group of 
Invertebrates may less easily find guidance than one who devotes 
his attention to such groups as Birds and certain Orders of Insects 
But it is my object to show that the careful observation of some of 
the commonest and most readily determined Invertebrates not only 
has in the past resulted in important additions to our knowledge, 
but is still capable of leading to results of great interest. 
As an illustration of the advances made in the past along these 
lines, I will direct your attention to two British Naturalists, 
John V. Thompson and Sir John Graham Dalyell, who will 
always take an honourable position in the history of the study 
of Marine Invertebrates. Most of Thompson’s results appeared 
in the form of a few short memoirs entitled ‘Zoological Researches,’ 
published at Cork from 1828 to 1834. Short as these papers are, 
they contain a surprising amount of most important work. In 
the first memoir (1828) Thompson quotes the opinion of Dr. Leach 
that the higher Crustacea undergo no metamorphosis, and proceeds 
to show that this is so far from being the case that exactly the 
opposite statement should have been made. The organism known 
