11 



restricted to an area situated at one of the poles in place of 

 being scattered equally all over. The Nassellaria agree with 

 the Spumellaria, and differ from the Acautharia in possessing 

 a siliceous skeleton. 



The Phaeodaria are the most divergent and most highly 

 differentiated group of the Kadiolaria. They may be con- 

 sidered as derived from Phceodina, an ancestral form which 

 has arisen from Actissa by a considerable amount of modifi- 

 cation. The capsule membrane became double, and the 

 pores probably first became restricted to one pole, and then 

 this porous area was modified into a single opening provided 

 with a radiated operculum. Two small accessory openings at 

 the opposite pole of the capsule may also be present. A 

 peculiar pigment body (the phseodium) became developed 

 outside the capsule membrane, close to the principal open- 

 ing. These characters are found throughout the Phaeodaria, 

 and the majority of the group possess in addition a skeleton 

 formed of hollow siliceous bars, a feature distinguishing them 

 from all other Radiolaria. 



The Metazoa, to which we must now pass on, includes 

 the animals above the Protozoa, and may be distinguished by 

 two important characteristics : — 1. The body is always 

 multicellular, being formed of more than one cell, usually of 

 a very large number. The few Protozoa which are composed 

 of more than a single cell (such as some of the Infusoria — 

 see fig. 6), are clearly colonies formed of a number of inde- 

 pendent members, each of which is unicellular. 2. Repro- 

 duction, though it may also be effected by budding, or some 

 other asexual method, is always performed sexually by ova 

 and spermatozoa ; while in the Protozoa, these reproductive 

 elements are not found, and consequently true sexual repro- 

 duction cannot take place. These two characters might be 

 considered as one, since the second really depends upon the 



