THE WONDERS OF LIFE 



less (rest-spores or paulospores) ; sometimes they have 

 one or more lashes which enable them to swim about 

 (rambling - spores or planospores). This monogenetic 

 propagation is very common among the protists, both 

 protophyta and protozoa. Among the latter the sporozoa 

 (gregarinae, coccidia, etc.) are remarkable for the passing 

 away of the whole unicellular organism in the formation 

 of spores; in this case and in many of the rhizopods 

 {mycetozoa) the process coincides with manifold cell- 

 division. In other cases (radiolaria, thalamophora) only 

 a portion of the parental cells is used for the production 

 of spores Spore-formation is very common among the 

 cryptogams ; here it usually alternates with sexual prop- 

 agation. The spores are generally formed in special 

 Spore-capsules (sporangia). In the flowering plants 

 (anthophyta) sporogony has disappeared. It is found 

 at times in the tissue-animals (in the fresh -water sponges) ; 

 in this case the sporangia are called gemmulcB. 



The essential feature of sexual generation is the coa- 

 lescence of two different cells, a female ovum (egg-cell) 

 and a male sperm-cell. The simple new cell which 

 arises from the blending of these is the stem-cell (cytula), 

 the stem-mother of all the cells that make up the tissues 

 of the histon. But even among the unicellular protists 

 we find in many places the beginnings of sexual differen- 

 tiation ; it is foreshadowed in the blending or copulation 

 of two homogeneous cells, the gameta. We may con- 

 ceive this process, or zygosis, as a peculiar and very 

 favorable kind of growth, that is connected with a 

 rejuvenescence of the plasm; the latter is enabled to 

 propagate by repeated cleavage through the mixing of 

 the two different plasma-bodies on either side {am- 

 phimixis) . When these two gameta become unequal and 

 differ in size and shape, the larger female body is called 

 the macrogameton or macrogonidion, and the smaller, 

 male part, the microgameton or microgonidion. Among 



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