Mermis Parasitic on Ants of the Genus Lasius. 365 



II. Desckiption of Mermis myrmegophila sp. nov. — 



H. A. Baylis. 



General Characters of Adults and LarvsR. 



The worms are colourless, with the exception of a slight tinge 

 of reddish-brown near the head in some specimens. The cuticle is 

 smooth externally, but provided with criss-cross fibres below the 

 surface. It consists of a thin outer and a thick underlying layer. 

 The subcuticular layer (fig. 10, sc}j is very thin, and gives rise to the 

 six longitudinal bands or " fields " characteristic of the genus 

 Mermis, sensu stricto. These consist of a pair of very broad and 

 conspicuous lateral fields, a pair of very slender subventral, a 

 broad ventral and a narrow dorsal field, the last-mentioned being 

 subdivided into three parallel portions (fig. 10, d.). The cells com- 

 posing the lateral fields are very conspicuous (fig. 9), consisting of 

 a row of large, tall, granular cells at the edges, fitting together 

 like pieces of a mosaic, and an irregular double row of smaller 

 cells in the middle, with clearer protoplasm. 



The musculature of the body-wall (fig. 10, m.)is divided by the 

 longitudinal fields into six broad strips, each of which is composed 

 of a large number of narrow, ribbon-like muscle-cells with one 

 edge hanging freely in the body-cavity. 



Almost the whole of the body-cavity is occupied by the " fat- 

 body," representing the degenerate intestine of the worm. This is 

 simply a sausage-like sac, blind at each end, consisting of a thin 

 membrane enclosing an accumulation of fat-like globules of reserve 

 food-material. As the worms increase in size and age, this reserve 

 material is gradually absorbed. In the earlier stages, however, it 

 is so abundant as to render the worms very opaque, and their 

 structures difficult to make out. 



The mouth is subterminal, being situated towards the ventral 

 side of the head, in a shallow cuticular depression. The 

 oesophagus, as is usual in the later stages of Mermithidte, is 

 vestigial, being reduced to a long, narrow, cuticular tube. It is 

 doubtful whetlier it is connected with the fat-body at all. As 

 is the rule among Mermithidee, there is no anus. 



The nervous system is of the usual kind, the central ganglia 

 being situated in a broad ring of nervous tissue which surrounds 

 the oesophagus at some little distance from the head. No excretory 

 organ has been made out. 



We have no information as yet as to the earlier stages in the 

 larval history of the worm. It is probable that the young larvte 

 penetrate into the body-cavity of the larvte of the ants, and remain 



