128 
ON THE STRUCTURE AND HABITS 
ocean. In Britain it rarely occurs. It is the largest of the genus, exceeding 
many of the Gulls in size. Feeds on fish, mollusca, Crustacea, &c. The eggs, 
four in number, are laid in a hollow scraped on the sea-shore. Breeds on the 
shores of the Black Sea, the Baltic, &c. The young are transversely barred with 
brown ; in adults the crown of the head, white in winter, becomes black in 
summer, and one description will suffice for the plumage of both sexes. 
Here, then, endetli our analysis of Part XVIII. of this splendid and valuable 
work. 
Campsall Hall, Oct. 26, 1838. 
REMARKS ON TPIE GENERAL STRUCTURE AND HABITS OF 
INVERTEBRATE ANIMALS * 
By Edwin Lankester, M.R.C.S. 
(Concluded from Yol. III., p. 410.) 
The classes of animals which have been previously noticed, will be found to be 
Cycloneurose and Cyclogangliate sub-kingdoms. I shall now commence with 
those classes found in the Byploneurose group, where the nervous system is 
arranged in a double line along the fore part of the animal. 
Many of your readers have probably, in passing a venerable Oak, or a spreading 
Elm, observed that their bark is covered with a greenish scaly substance, which 
s one of the lower tribes of plants, a Lichen. Many other kinds of plants fix 
themselves to the trunks of trees in this manner; some of them, as the Boleti 
and the Mistletoe, deriving all their Nourishment from the plant on which they 
grow. Now precisely the same thing occurs in the animal kingdom, for as we 
have plants living on living plants, so we have animals living on living animals; 
and the next group of animals which falls to our consideration is one of this 
kind. They are called Entozoa , and vary exceedingly in their size, shape, and 
form. No animal is free from these invaders ; the higher we ascend in the scale 
of organisation, the more abundant do these pests become; and Man is more 
obnoxious to them than any other creature. They are, however, generally con¬ 
cealed, either by their size or situation, from the eye, and justify the language 
of the poet— 
* Being the substance of a lecture delivered at the Doncaster Lyceum, Oct. 15, 1838, Mr. J. B. 
Testa in the chair. 
