274 ESSENTIALS OF ZOOLOGY 



colonial genera. Vorticella and Carchesium have contractile stalks 

 while Epistylis is attached by noncontractile branching stalks. 



The second subclass, Suctoria or Tentacnlifera, as it is sometimes 

 called, includes animals that are not ciliated, except during a free- 

 swimming stage which may occur following division or encystment. 

 These are attached forms with protoplasmic projections which are 

 used in the capture of food. Most of them are marine, but Podophrya 

 is an example of a fresh-water genus. This subclass is frequently 

 given the standing of a class, giving the phylum five classes. 



4. Class Sporozoa (spo rO zo' k, seed animal). — These protozoans 

 in their early stages are often amoeboid, but in the completed life 

 history locomotor structures are wanting. During the life cycle there 

 is a spore stage. The animals of this class are entirely parasitic 

 and they are usually transmitted to other animals in the spore 

 stage. They often pass from one host in its feces and enter another 

 in contaminated food or drink; or they are drawn from one host by 

 a blood-sucking animal and transmitted to the blood of another. 

 All Sporozoa reproduce by sporulation in which asexual, multiple 

 fission is followed by gamete formation, and the gametes fuse to 

 form a zygote. The spores are produced by the parent animal 

 dividing into fragments while it is encysted. These little cysts, 

 which are secreted by the protoplasm of the animal, are protective 

 and enable them to withstand adverse conditions. The cyst is dis- 

 solved upon entrance to a host and liberates the organisms. 



This class of Protozoa is among the most widely distributed of 

 the animal parasites, and their life cycles are often quite compli- 

 cated. There are three subclasses of the class, and each of these is 

 divided into some orders. The first subclass is Telosporidia in which 

 the spores produced have neither a polar capsule nor polar filament. 

 In this group are three orders, (a) Gregarinida, commonly called 

 gregarines, inhabit the cells (cystozoic) of earthworms, cockroaches, 

 other insects, and occasionally vertebrates in their early stages, but 

 later they may become free in the cavities of the host. They may 

 attain considerable size, (b) Coccidia are minute monocysted forms 

 which are permanent intracellular parasites of molluscs, arthropods, 

 and vertebrates, including man. The life history involves a period 

 of asexual reproduction (schizogony) and a period of so-called sex- 

 ual reproduction which ends in spore formation (sporogony). (c) 

 Haemosporidia. The representatives of this order live chiefly in the 



