436 FAUNA HAWAIIENSIS 



in all directions by a series of tubes or lacunae which have no definite lining, but which 

 seem to be mere splits in the fibrillar matrix. The lacunae — except in the head — have a 

 general circular direction which is very well marked in the trunk region where each runs 

 into a lateral longitudinal split (figs. 20 and 24). They contain a small amount of coagu- 

 lum, the remnant of the fluid which circulates in them ; during life this fluid, in other species, 

 holds in suspension fat and coloured oil globules. If these are present in my species 

 they must have been dissolved out in the processes which precede embedding. The 

 circular lacunae of the trunk not only communicate with one another by means of the two 

 longitudinal lateral lacunae (figs. 20 and 24), but they open into one another by numerous 

 small branches which have an oblique or longitudinal direction. In the head the lacunae 

 have a general longitudinal course ; they are not, however, straight, but twist in and out 

 between the pits on the surface ; they anastomose freely (fig. 14). Thus in a transverse 

 section of the head the lacunae appear as round holes more or less uniformly arranged 

 in the skin, and the same effect is produced by a longitudinal section of the trunk. 



In the collar region the subcuticular tissue is much thickened, and the lacunar 

 system forms a single more or less definite ring which gives off numerous branching 

 anastomosing twigs (fig. 15). 



Although the above account attempts to give the general course of the lacunae in 

 the skin, it should be mentioned that there is considerable irregularity in the arrange- 

 ment, and one is almost inclined to believe that the canals do not remain permanent, 

 but that they sometimes close up and new ones appear. As they have no lining of any 

 kind, such a closing would leave no trace. 



As Schneider^ Hamann", and Kaiser' have shown in the species investigated by 

 them, the lacunar system of the introvert is completely shut off from that of the neck — 

 if it be present — and of the trunk, by a fold inwards of the cuticle which cuts the 

 subcuticular tissue in two. I have not been able to find any such cuticular ring in the 

 species in question, but the state of preservation of my specimens does not allow me 

 to say definitely that it does not exist. 



The lemnisci are two elongated sac-like prolongations of the subcuticular tissue 

 which are attached anteriorly to the skin at the junction of the head and collar. They 

 extend backwards to the extreme posterior end of the body, and are slightly bent so 

 that a longitudinal section may cut them in two or three places (fig. 23). Histologically 

 they are composed of the same substance as the subcuticle in direct continuity with 

 which they arise, and they are traversed by a similar system of canals. Physiologically 

 they seem, as Hamann suggests, to act as reservoirs for the fluid of the canal system of 

 the introvert ; when the fluid they contain is forced into the spaces of the introvert the 

 latter is everted. It is withdrawn again into the body by special muscles. In most 



' Arch. Anat. 1868, p. 584. 



° Die Nemathelminthen, Heft i and 2, Jena, 1891 and 1895. 



' Bibl. Zool. Heft 7, 1892, p. i. 



