A NEW SPECIES OF PENTASTOMUM. 167 



margin, in the middle line, can be readily seen, even with the naked eye, a 

 circular or slightly oval mark ; this is the line which indicates the boundary of 

 the oral papilla (woodcut, fig. 2). On either side of it are two slits, about 0*5 

 mm. in length, whose anterior extremities converge towards the middle line ; 

 these are the orifices of depressions of the cuticle which contain the hooks, 

 and the points of these may generally be seen, under a low magnifying power, 

 protruding from them. 



The orifices of the sexual glands are somewhat difficult to observe, but in 

 many cases they can be made out by careful examination, after the spirit has 

 been allowed to evaporate from the specimens. The male genital openings are 

 two in number, and are situated about 1 mm. behind the mouth, close to the 

 middle line, and one at either side of it (PI. XXVII. fig. 1, g.o). The female 

 genital apparatus opens also in the middle ventral line, but within less than 

 1 mm. of the posterior extremity. All three are perfectly simple orifices, with- 

 out any prominence. 



These were all the points worthy of note observed on the external surface. 

 I could find no tactile papillae, such as are to be seen in Linguatida tcenioides, 

 i although I looked for them with great care. 



The Body-Wall. 



The wall of the body consists of three distinctly marked layers — 



1. The Cuticle. 



2. The Epidermis. 



3. The Subepidermic Layer. 



1. The Cuticle (PL XXVII. fig. 9, cu) is a thin even layer which covers 

 the whole surface of the body, including the invaginations in which the hooks 

 are situated, and sends inwards prolongations which line the oesophagus, the 

 rectum, and the genital ducts. Its thickness is on the average about 001 mm., 

 and presents no noteworthy changes in different parts of the body, except that 

 it is slightly thinner in the invaginated portions. 



There can be little doubt, from the analogy of different forms of life, that 

 it is composed of chitin, although I attempted no investigation on this point, 

 beyond ascertaining the fact that it did not dissolve in boiling solution of 

 caustic potash. It is to all appearance quite structureless, even when 

 examined under high powers of the microscope ; no trace could be found of 

 the pores mentioned by Leuckart in L. tamioides* nor did the cuticle appear 

 to be divided into two distinct layers, which was probably owing to the. 

 immaturity of the specimens. 



* Bau u. Eutivick. d. Pentastomen, Leipzig u. Heidelberg, I860, p. 30. 



