Unicellular^ Microscopic Animals 363 



Coordination and Sensory Equipment. — The thousands of body cells 

 in the colony are connected by protoplasmic strands (Fig. 175) to estab- 

 lish physiologic (functional) continuity between these cells. Through 

 these structures, coordination between the various parts of the colony 

 may be accomplished. Most body cells contain an eye spot (stigma) 

 which is light sensitive and probably assists in orientation for photosyn- 

 thesis. 



Reproduction. — Reproduction occurs by asexual and sexual methods. 

 In asexual reproduction, certain cells of the colony without flagella in- 

 crease in size and are called parthenogonidia (par then o go -nid' i a) 

 (Gr. parthenos, virgin; gonos, offspring; idion, diminutive). These di- 

 vide to form numerous cells which form a new colony. This method of 

 developing an egg without unioji with a sperm is known as partheno- 

 genesis (par then o -jen' e sis) (Gr. parthenos^ virgin; genesis^ origin or 

 descent) . 



The sexual method consists in the formation of flagellated male sperm 

 and nonflagellated female eggs. Within the colony, certain cells, by 

 simple division, form a sperm bundle which may contain over 100 

 spindle-shaped sperm (male gametes). Other cells divide and produce 

 as many as 50 large eggs (female gametes). One sperm fuses with 

 (fertilizes) an egg (inside the colony) to form a zygote (zygospore) 

 which surrounds itself with a resistant wall to withstand the winter. 

 When proper conditions are encountered, the zygospore breaks the wall 

 and by division forms a new colony. In Volvox the colony consists of 

 two types of cells; the true somatic body cells and the true reproductive 

 germ cells (either male or female) . 



PLASMODIUM 



Plasmodium (plaz -mo' di um) (Gr. plasma, mold or form; eidos, 

 like) belongs to the class Sporozoa because it reproduces by means of 

 spores. Plasmodium vivax (vi' vax) (L. vivere, long live) causes the 

 so-called tertian type of human malaria (L. tertianus, thrice) with an 

 attack of fever every forty-eight hours (third day) ; P. malariae causes 

 quartan malaria (L. quartus, fourth) with an attack every seventy-two 

 hours (every fourth day); P. falciparum (L. falix, sickle) produces 

 aestivo- autumnal malaria (L. aestivus, summer) with daily attacks or 

 more or less constant fever. The life cycles of these three species of 

 Plasmodium differ only in minor details. Malarial fever is transmitted 

 by the bite of the diseased female mosquito (not the male) of certain 



