150 NEMATHELMINTHES chap. 



Crep. occurs in horses, twisted in a spiral round tendons and 

 muscles, forming tumours which require to be opened. 



V. Family Mermithidae. 



Nematodes without anus and with six mouth papillae. Two 

 spicules in the males and three rows of numerous papillae. 



Genera : Mermis, Bradynema, Atractonema, Allantonema, 

 Spliaerularia, and others. 



As a rule the Nematoda show but little trace of their parasitic 

 mode of life, but in this family there is considerable degeneration, 

 and in extreme cases the body of the female is reduced to a simple 

 sac crowded with eggs. They are exclusively parasitic in insects. 

 In some respects their structure shows a transition towards 

 Nectonema and the Gordiidae ; especially is this the case in the 

 structure of their ventral nerve-cord. 



The sexual form of Mermis nigrescens Duj. 1 lives in damp 

 earth, and after storms and in the early morning is sometimes 

 found in such numbers crawling up the stalks of plants, as to 

 give rise to the popular idea that there has been a shower of 

 worms. The male is unknown ; the female lays her eggs in the 

 ground, and there they hatch out. It is not known exactly how 

 the larvae make their way into the grasshoppers in whose body- 

 cavity they live, but in an allied species, M. albicans v. Sieb., 

 the larvae have been observed boring their way into small 

 caterpillars through their skin, and it seems probable that the 

 larvae of M. nigrescens burrow in a similar way into young 

 Orthoptera. 



Bradynema rigidum Leuck. 2 is found in the adult stage living 

 freely in the body-cavity of a small beetle Aphodiusfimetarius, one of 

 the Scarabeidae, from two to three to as many as thirty being found 

 in one host, which does not seem much injured by their presence. 

 The parasite is without mouth, anus, or excretory pore. The 

 eggs hatch out in the uterus of the mother, and the larvae are 

 male and female ; they make their way into the body- cavity of 

 the host, and here they pass an unusually long time, five months, 

 soaking in osmotically the nutriment contained in the blood 

 of the insect. Eventually they burrow through the walls of 



1 v. Linstow, Arch. mikr. Anat. vol. xl. 1892, p. 498. 



2 zur Strassen, Zeitschr. wiss. Zool. vol. liv. 1892, p. 655. 



