PROTOZOA. 263 



Mollusca are usually included in one of these classes, 

 although subdivided into groups of Mollusca propria, and 

 Molluscoida, the latter consisting of Polyzoa and Tunicata. 

 There is, indeed, a general relation between the Annulose 

 and Molluscous sub-kingdoms. 



Cephalous Mollusca are divided into the following classes : 

 1, Gasteropoda branchiata ; 2, Gasteropoda pulmonata; 

 3, Pteropoda ; 4, Cephalopoda. The last present us with 

 modifications of organisation in the Nautilus, Ammonite, 

 Belemnotenthis, <fcc. 



It would occupy too much of our space to give the 

 numerous subdivisions into which the classes and families 

 are broken up ; we beg therefore to refer the reader to the 

 works of Professor Owen, and Professor Bymer Jones, on 

 the Animal Kingdom, or Mr. Gosse's Manual of Marine 

 Zoology, 



In these and other valuable voluminous treatises on 

 this interesting department of nature, the above division 

 is strictly adhered to ; but as our object is to give a popular 

 account of the wonders disclosed by the microscope, we 

 will not closely follow the path of the learned investigators 

 of this branch of science ; but avoid as much as possible 

 the adoption of terms so often alarming to the unini- 

 tiated, culling, as we pass, from objects of the greatest 

 interest, and likely to create a desire for further know- 

 ledge, whereby there will be found a future pleasure in 

 overcoming the obstacles, by which the learned render so 

 mysterious to the popular mind, the stores of their 

 gathered wealth. 



PROTOZOA. 1 



Gregarinida present us with the simplest form of all the 

 Rhizopods. A gregarina is a simple mass of granular, and 

 usually transparent, substance, whose outer boundary pre- 

 sents, more or less distinctly, the aspect of a membrane, 

 while its interior contains a clear spheroidal space, in the 

 centre of which is a nucleus-like particle ; so that the 

 whole animal has a remarkable resemblance to an ovum. 



(1) Mr. Huxley divides the Protozoa into two great groups : 1. The Astomata, 

 or those which are unprovided with any permanent oral aperture Gregarince, 

 Rhizopoda, Sportf/iadce, Thalassicollidce. 2. The Stomatoda, whi' h have a per- 

 manent oral aperture, and the rudiment of an alimentary canal 1,-j'usoria^ Noc- 

 tilucidce. 



