PROTOZOA. 19 



present in considerable numbers ; these, however, are 

 non-contractile and inconstant in position. The pseudo- 

 podia branch and anastomose. Food material diatoms 

 and the like is found in the protoplasm of the body. 

 The adult draws in the pseudopodia and covers itself with 

 a cyst (PI. 7, fig. 9). A structureless, glassy membrane 

 surrounds the orange-red contents. PL 7, fig. 10, repre- 

 sents another stage more advanced in which the interior 

 mass has become divided into many orange-red balls. In 

 PL 7, fig. 1 1, the cyst has opened and the flagellate young 

 are issuing. This completes the cycle of the life of the 

 Protomyxa. 



PL 7, fig. 12, is an under-fed adult. We describe it 

 here as an illustration of the fact that unfavorable condi- 

 tions produce changes in structure which may tend 

 towards the reduction of the zoon. The vacuoles have 

 decreased in number and the pseudopodia only slightly 

 branch and anastomose. The structural changes induced 

 by the small quantity of food taken may be transient, as 

 in the case figured above where the under-fed zoon might 

 become like the over -fed specimen (PL 7, fig. 8) by giv- 

 ing it a larger supply of food. If, however, the cause of 

 structural change, be it an insufficient diet or any other 

 cause unfavorable for the development of the zoon, were 

 continued through successive generations, the result prob- 

 ably would be the production of a smaller, weaker, per- 

 haps distorted form, and finally the total extinction of the 

 species. Such a species may be called a reduced or a 

 suppressed species, since it has suffered diminution in 

 organs and efficiency. It is also often called simple, but 

 in order to avoid the mental confusion which arises when 

 this word simple is applied both to primitive and to 

 reduced forms, we prefer to restrict its use to the former 

 which have comparatively few organs and these oftentimes 

 in rudimentary or developing condition. There are oth( r 

 reasons for doing this. While it may be true that there are 

 reduced animals which cannot be distinguished from the 

 primitively simple forms, yet in the great majority of 



