Iviii INTRODUCTION 



infusorian : — a view which continued to subsist down to the 

 early researches of KoUiker. 



His second class is that of polyps, the first order of which 

 is the rotifers : among them he includes Vorticella, which is 

 a real infusorian. The second order include the polyps, which 

 form polyparies. This corresponds to a mixture of Hydro- 

 zoa and Anthozoa with Polyzoa. It includes the sponges 

 as one genus, a few Algae, including Corallina, an echinoderm, 

 an arthropod, the ascidian Botryllus, etc. The last genus 

 of polyps, the genus therefore which Lamarck regarded as 

 having advanced farthest in development, is the sea-anemone. 



Lamarck's third class are the radiarians, with two orders. 

 The first order, or soft radiarians, contain all varieties of 

 coelenterates, except Anthozoa. They are grouped together 

 on account of their radiating structure, with the medusa as 

 a type. This order includes also the tunicate Pyrosoma. 

 The second order of radiarians are the echinoderms. La- 

 marck includes Sipunculus — a gephyrean — as an echino- 

 derm, on account of its resemblance to holothurians : and 

 this classification was still retained as late as 1841 by Forbes 

 in his British Starfishes. It constitutes Lamarck's highest 

 genus of radiarians. 



Class IV. contains the worms, divided into three orders 

 of round worms, bladder-worms, and flat-worms. Among 

 the latter is included Linguatula (an arthropod), and Fasciola 

 already mentioned. The round worms are chiefly nematodes, 

 but include also turbellarians, cestodes, etc., and one genus 

 " Scolex " (the tape-worm's head). Among the bladder- 

 worms is placed an animal under the name of bicorne. On 

 reference to the Animaux sans Vertebres, I find it alluded 

 to as Ditrachyceros. I believe that the separate segments of 

 tape-worms were referred to under this name, being taken for 

 independent individuals. At a certain stage, the segments do 

 sometimes show two horn-like processes. 



Class V. contains the insects, divided into much the same 

 orders as at the present day.^ The next higher class, Class 



' There are a few minor inaceuraoies, such as the statement that the Hemiptera 



