154 



The Journal of Heredity 

 ad in 



mphl 

 mph^\ \\ 



mphl—. 

 amph2~j^ 



amphSf 



VARIATIONS IN HEAD ORGANS IN SPECIES PRODUCING INTERSEXES 



Figure 9. The head organs of most species of nematodes are very constant in form and 

 position. The function of the amphids {Amph 1-3) is not definitely known, but there is 

 reason to believe that they are chemical sense organs. The fact that they are so similar 

 on dififerent individuals of the same species makes them of great value in the systematic 

 classification of nematodes. In the case of Ag. dccaudata, however, we find a striking ex- 

 ception to this rule, for great variation is observed in the number and position of the 

 amphids. This is further evidence of the existence of numerous closely related species which 

 intercross in nature. Antlli, amphid ; c\it in, cuticular incision between the papillae of the 

 left and the right side. 



forms, l)y Bridges in mutants of 

 Drosophila inclanot/asfcr and by Sturte- 

 vant in Drosopliila simulans. In all 

 these cases intersexes resulted from 

 hybridization of closely related geno- 

 types. Are there signs that also in 

 our ca.se the observed intersexes could 

 be the result of hybridization of 

 races or genotypes closely related and 

 living mixed with each other in nature ? 

 'j'his appears to be the fact. Many 

 diffictilties arose as I tried to identify 

 the material bnjught to me. In the 

 taxonomy of nematodes the structure 

 of the head end and chiefly the organ- 



ization, the location and number of 

 the head sense-organs are of high im- 

 portance. This is particularly true in 

 the Mermithids, where other characters 

 for the distinction of the species are 

 very few in number and many of them 

 to he seen with great difficulty or only 

 on adult specimens. Therefore, a close 

 study of the head end and its sense- 

 organs is absolutely needed for a good 

 identification. There are two kinds of 

 head sense-organs in most of the nema- 

 todes — the papillae, which are claimed 

 to be organs of touch, and the amphids 

 (Cobb) or lateral organs, which are 



