248 CONSIDERATIONS OF CLASSIFICATION AND METHODS 



of heredity, the spirochaetes having been found in the ovary and ova of the fema 

 tick. 



9. Heterogenesis, Parthenogenesis. Offspring differs from parent, but after 

 one or more generations there is reversion to the parent form. 



Strictly speaking the term heterogony applies to reproduction when a sexual 

 generation alternates with a parthenogenetic one. Where a nonsexual genera- 

 tion, as by division or budding, alternates with a sexual one the process is called 

 metagenesis. In parthenogenesis reproduction eggs develop without the occurrence 

 of fertilization by spermatozoa. 



In coccidiosis we have a sexual cycle (sporogony) alternating with a nonsexual 

 one (schizogony) . In the infection with Strongyloides we have a sexual cycle 

 alternating with a parthenogenetic one. In malaria we have a sexual generation, 

 a nonsexual one and according to Schaudinn, a parthenogenetic one, which latter 

 accounts for malarial relapses. 



10. Homology and Analogy. By homology we understand the anatomical 

 correspondence of the organ of one animal to that of another. Thus the foreleg of 

 a quadruped and the wing of a bird are homologous organs. Analogy refers to 

 physiological or functional agreement, thus the lungs of mammals and gills of fish, 

 both with respiratory functions, are analogous organs. The first trace or appear- 

 ance of an organ in an embryo is known as the anlage of the organ. 



11. Protista. Haeckel proposed this name for unicellular animals and plants, 

 thus including protozoans and protophytes in a kingdom separate from the animal 

 and vegetable kingdoms. 



We have sufficient difficulty in drawing the line between an animal and vegetable 

 organism so that to make a demarcation of a new kingdom from the two usually 

 recognized would add to our difficulties. 



nale 



