THE DISAPPEARANCE OF THE MALE MONONCH 



OF ALL the nematodes or thread- 

 worms, few are more common 

 than the Mononch. Its micro- 

 scopic size conceals its abundance. 

 Hundreds of milUons of them may be 

 found in a single acre of garden soil. 

 Dirt is usually thought of as dead 

 matter, but to a magnifying eye it 

 would appear to be almost alive, a 

 squirming mass of- micro-organisms, 

 abundant among which would be the 

 Mononchs, benefiting the agriculturist, 

 by rapaciously destroying many other 

 nematodes and micro-organisms that 

 injure plants. 



The remarkable sexual history of 

 these nematodes is described by N. A. 

 Cobb (Contributions to a Science of 

 Nematology, VI, Soil Science, May, 

 1917). In most mononchs males are 

 either nonexistent or else so rare as to 

 be negligible, a single one occurring 

 perhaps among several thousand 

 females. In these circumstances, the 

 male has ceased to play an important 

 part in reproduction, and the female 

 has developed the capacity to produce 

 sperm and ova in the same organ — a 

 condition that Dr. Cobb calls syngonism. 

 Early in her life the female produces a 

 quantity of spermatozoa, which are 

 stored away by her. Later the female 

 sexual characters develop and she 

 produces ova, which are fertilized by her 

 own, exceedingly minute spermatozoa. 

 In some nematodes the spermatozoon 

 seems merely to give a stimulus to the 

 egg, which then develops ])arthcno- 

 genetically; but in those studied by Dr. 

 Cobb it seems likely that there is a real 

 fusion of the two sex-cells, which, 

 therefore, probably differ in the same 

 way that the male and female reproduc- 

 tive cells of other animals do. It is 

 possible. Dr. Cobb suggests, that in 



other animals where the ovum is thought 

 to develop without fertilization, it may, 

 in reality, be fertilized by a very minute, 



// 





XIOOO 



A MONONCH 



Garden soil is full of microscopic thread- 

 worms like this. The head of the speci- 

 men here figured is accurate in every 

 detail; the body is somewhat posed. Its 

 mouth is wide open, showing its promi- 

 nent single fang. It feeds on other thread 

 worms. From a drawing by W. F. 

 Chambers. (Fig. 20.) 



hitherto overlooked spermatozoon pro- 

 duced by the female herself, just as in 

 the case of the Mononch. 



4M 



