6 Outline of Life-history 



either a Gordius or a Mermis. In its first condition it 

 infests the larva, but a later stage has been found in the 

 pupa and in the newly emerged fly, coiled in the body- 

 cavity about the abdominal viscera. At length the worm 

 quits its host, and then lives free in the mud, attaining a 

 length of about an inch. The sexes are distinct, the male 

 being distinguished by a spicule near the end of the tail. 

 The intestine runs almost the wliole length of the body, 

 and is at first filled with grannlar matter. It ends 

 blindly at both ends. An oesophagus extends backwards 

 for some distance from the head-end, but does not enter 

 the intestine '. The eggs are formed within a convoluted 

 tube, but ultimately escape into the body-cavity, wdiich 

 they distend to such a degree that the female worm 

 becomes little more than an egg-sac. What appears to 

 be the outlet of the female reproductive organs is distant 

 about one-third of the length of the body from the head. 

 In the mature male the testis extends along nearly the 

 whole 1 ■ngth. The spicule is imperforate, and no outlet 

 to the rej)roductive organs has been discovered. A double 

 row of minute papillae runs along the inside of the curved 

 tail, near the spicule. These seem to be glandular, 

 for slight pressure (e, g. the weight of a cover-glass) 

 causes them to exude a viscid fluid, which takes the form 

 of threads mingled with loose cells. These occupy all 

 the centre of the close coil formed by the tail, while the 

 spicule is protruded (fig. 3, 2). Neither the double spicule 

 of the male Mermis nor the cleft tail of the male Gordius 

 was seen. 



The following species are said to infest Chironomus : — 

 Gordius tolosanus, Duj., Mermis albicans, 8ieb., 31. acu- 

 minata, Sieb., 31. chironomi, Sieb., 31. crassa, Linst. 

 They are parasitic on the larva and pupa, and 3Iermis 

 albicans at least is not uncommon in the fly. The 

 identification of the species in the second larval stage 

 is difficult, and we have often been in doubt as to the 

 forms observed. 



Those who make many sections of Chironomus -larvae 

 and pupae will be sure to come across specimens which 

 harbour Gordian worms, and it may save them much 

 time if they bear this in mind. It has happened to us to 

 waste many hours over a singular new structure which 

 at last revealed itself as a Gordius. 



' A similar break of continuity has been described in Mermis. 



