NOTES ON THE FREE-LIVING NEMATODES. 477 



There are, ])owever, some indications that it is not tlie 

 female alone which is capable of developing- a hermaphrodite 

 gonad. luRhabditis elegans Maupas records (pp.491— 

 492, PI. X.V11, fig. 2) the occurrence of large egg-like cells 

 in the testis. A similar phenomenon has frequently been 

 i-ecorded as characteristic of the normal male gonad in 

 Crustacea (Orchestia), and in other Crustacea the appear- 

 ance of eggs in the testis, without doubt to be attributed to 

 the indirect action of parasites, is so definitely associated 

 with the development of female secondary sexual characters 

 as to indicate a change to hermaphroditism. In Rhabditis 

 elegans the phenomenon is very slightly manifested, but 

 there are indications that a very much more complete change 

 is imposed on the male of Bradynema rigidum, a nema- 

 tode parasitic in the body-cavity of the beetle Aphodius 

 fimetarius.i This animal is so adapted for its parasitic life 

 that mouth and anus have disappeared, and the aliuienturv 

 canal, in the larva represented only by a single column of 

 cells, has left not the slightest trace in the adult. In the 

 autumn immense numbers of larv£e (up to '51 mm. in lengtl)) 

 are found in company with one or two adults in each host. 

 These larvae may be divided equally into females, whose 

 genital glands, paired and situated in the middle of the body, 

 have only attained to a rudimentai-y development, and males 

 (Text-fig. 11, a), in which the testis, situated posteriorly in 

 the body, often contains mature spermatozoa. When in this 

 stage the larvas bore through the walls of the alimentary canal 

 and disappear. No intermediates are known between these 

 forms and the adults 3-5i mm. in length, with a single excep- 

 tion to be described later. In the adult condition thei'e is only 

 one class of individual with a long and vastly convoluted gonad 

 opening to the exterior in the very posterior position which 

 is occupied by the anus, in nematodes with a functional 

 alimentary canal. It is this circumstance which led zur 

 Strassen to derive the adults from the male larvae, for if they 

 are developed from female larv^ there must have occurred a 

 1 Zur Strassen, ' Zeitschr. f. wiss. Zool.,' t. 54, 1892, pp. 656-747. 



