22 INBREEDING AND OUTBREEDING 



asexual type of reproduction. In the arthropods, as well as 

 in some other forms, mechanisms arose by which the eggs 

 developed without fertilization. This partheiiogenetic 

 reproduction has been relatively successful, but only as a 

 stop-gap. Sexual reproduction persists and is used as an 

 occasional means of propagation. It would seem that it 

 possessed advantages too great to be given up entirely. 

 Even as sexual reproduction is a later method of 



propagation than asexual reproduc- 

 tion, hermaphroditism appears to be 

 a secondary development from forms 

 in which the sexes were separate 

 (gonochorism or dicecism). Omitting 

 the protozoa in which it is difficult to 

 decide such sexual differences, gono- 

 chorism is present in every great 

 animal group but the sponges, and 

 hermaphroditism everywhere except 

 in the Trochelminthes, although in 

 Nemathelminthes, Echinodermata and 

 FIG. 2. Asexual repro- Arthropoda it is rare. An extended 



duction by means of runners . , , . . , , 



in the hawkweed. (After experiment on the sumect ot hermaph- 



Andrews.) 



roditism certainly was made, but that 

 it was an experiment, that hermaphroditism is from the 

 evolutionary standpoint a secondary institution, is clear 

 if one considers the anatomical evidence, as is shown by 

 Caullery. 23 Generally, hermaphroditism is a condition 

 associated either with parasitism or with a sedentary life. 

 Furthermore, hermaphroditic organisms do not have a 

 truly simple organization. They have a superficial simplic- 

 ity, due to an adaptation to their mode of life, but if one 

 compares hermaphroditic and gonochoristic species group 



