Mermis Parasitic on Ants of the Genus Lasius. 371 



straight, and maintains almost the same diameter, throughout its 

 length. The blind, rounded terminations of the two ovaries are 

 situated at 6 '5 mm. from tlie anterior and 1*5 mm. from the 

 posterior end of the worm respectively. 



The fully-formed ova are of discoid or lenticular shape, with a 

 thin shell, measuring- 0* 045-0 -05 mm. in greatest diameter. At 

 the time of laying, the content of the egg consists of very granular 

 protoplasm, but is as yet unsegmented. When the eggs are laid 

 (fig. 12) they are surrounded by a coat of some clear secretion, 

 probably of an albuminous nature, which keeps each egg in the 

 mass apart from its neighbours, and prevents the shells from 

 coming into contact. 



Specific Diagnosis. 

 Mermis myrmecopJdla sp. n. 

 (? = Gordius formicaruni Diesing, 1851 — nom. nud.) 



Mermis : adult (female) up to about 50 mm. in length. Thick- 

 ness about 0*6 m.ni. Body tapering anteriorly, less so posteriorly. 

 Both extremities rather bluntly rounded. Head with two subdorsal 

 and two subventral papilhe, at the bases of slight conical cuticular 

 depressions, and two lateral organs, in the form of tubular depres- 

 sions in the cuticle, in the usual position of the lateral papillse. 

 Lateral fields wide, com^josed of two outer rows of large cells and 

 two inner rows of small cells. Mouth subventral. (Esophagus 

 at least one-quarter of the total length. Nerve-ring at about 

 57 mm. from the anterior end. Vulva slightly behind the 

 middle of the body. Uteri directly opposed. Ova colourless, 

 discoid, thin-shelled, 0-045-0 '05 mm. in greatest diameter, 

 surrounded at the time of laying by an external hyaline coat, and 

 with unsegmented content. The worms live in soil in wet places, 

 in the neighbourhood of nests of ants of the genus Lasius, in 

 tlie females of which the larva is parasitic. 



The species of Lasius in which the larvee have been found at 

 present are L. aliemts, L. flavus and L. niger. 



Among the nearest relatives of M. myrmecophila appear to be 

 M. pachysoma v. Linstow, 1905, recorded in Vespa germanica ; and 

 M. hrevis Hagmeier, 1912, recorded in Lulus sahUosus and in 

 various soil-inhabiting dipterous larvae, but also found in tlie free- 

 living stage under a nest of ants (Myrmica rubra). From 31. Irevis 

 the present species differs chiefly in its considerably greater size 

 and in the absence of the lateral pair of cephalic papillae in the 

 adult ; while there is little of diagnostic value in the description 



