MORPHOLOGY AND TAXONOMY OF THE SPOROZOA 541 



ing in couples to form isogamous or anisogamous gametes. Division 

 or asexual reproduction of any kind is unknown. Only exceptionally 

 are more, or less, than eight sporozoites formed in each sporocyst. 

 They are monocystid (single chambered) or polycystid in structure, 

 the former grouped in the Sub-order Haplocyta, the latter in the 

 Septata, 



Order 2. Schizogregarinida Leger (1892). 



The Schizogregarinida are parasites of the digestive tract and 

 appended organs of arthropods, annelids and tunicates. They 

 differ from the Eugregarinida in having an asexual or multiplicative 

 cycle, the sporozoite growing into an agamont either as an intra- 

 cellular or an extracellular parasite. Asexual reproduction occurs 

 by division, internal budding or by multiple division. The life 

 history, gamete formation and metagamic divisions of the zygote 

 vary widely and no characteristic difference marks the sporoblasts 

 from those of the Eugregarinida. Change of hosts is safely estab- 

 lished for only one type— the Porosporidae. 



Sub-class II. COCCIDIOMORPHA Doflein. 



While the Gregarinida are practically limited to invertebrate 

 hosts and are typically lumen-dwelling parasites, the Coccidio- 

 morpha are widely distributed in all groups of animals and are 

 typically intracellular parasites in all stages of growth and repro- 

 duction. Change of hosts with alternation of generations, while 

 by no means universal, is more common than in the Gregarinida. 

 Agamogony is characteristic of all types and leads to multiple 

 infection with frequently lethal results to the host due to the 

 destruction of multitudes of epithelial or blood cells, to thrombus 

 formation, or to the liberation of toxins. The life cycle varies 

 from relative simplicity to great complexity; gamonts become 

 differentiated into gametocytes which may be recognized as male 

 and female; gametes are anisogamous with rare exceptions; zygotes 

 give rise to sporoblasts which may (Coecidia) or may not (Herao- 

 sporidia) be protected by resistant membranes. 



Order 1. Coccidiida Leuckart Em. 



Sub-order 1. Eimeriina. 



Typically epithelial-cell-dwelling parasites, with exceptions, how- 

 ever, in Cryptosporidium muris Tyzzer, Eimeria mitraria Laveran 

 and Mesnil and Orcheiobiiix herpobdellae Kunze, which are lumen- 

 dwelling coecidia. 



Cellular differentiations are much less numerous than in the 

 gregarines; particularly is this true of the cortex. They are motion- 

 less forms without myonemes or other motile organs save flagella 



