REPORT ON THE NEMERTEA. 57 



lamellar connective tissue of the basement layer Bet, upon which the whole of the integu- 

 ment rests, may here be specially insisted upon, and is indicated in the same figures. 



Finally, I have to mention the two layers of fibres which, though very delicate, form 

 in Eupolia very constant and characteristic parts of the integument. They are imme- 

 diately applied against the inner surface of the supernumerary basement layer B — an 

 outer layer of circular and an inner one of longitudinal fibres. Fig. 9 {Eupolia 

 delineate/,, long, sec.) shows them to be more conspicuous than figs. 2, 3 {Eupolia 

 australis). Fig. 9 moreover, serves to demonstrate that the pigment, to which in this 

 species the peculiar longitudinal brown stripes are due, is accumulated in the same 

 stratum of the integument, where these fibrous layers are found ; the section represented 

 shows an unpigmented zone between two pigmented ones. The pigment is granular, and 

 appears to be limited to this stratum. It was not met with in the other species of Eupolia. 



That I am justified in looking upon the integumentary arrangement of Eupolia as a 

 higher differentiation of a lower type, which in general resembles the integument of Cari- 

 nina, must now be shown by a short account of the condition of things in Cephalothrix 

 and Carinoma, two other Palasonemertea, both of them inhabitants of the European seas. 



Cephalothrix shows an advance in differentiation upon Carinina, by the deeper 

 situation of the lateral nerve-stems (PI. XL fig. 15), imbedded in the outer longitudinal 

 muscular layer. Still it deserves special attention, that in this genus the medio-dorsal 

 nerve is still situated in the deepest layer of the integument (PI. XL fig. 5) outside 

 of the basement membrane, and that, at the same time, the integument wholly answers 

 to the description that we have given of the integument of Carinina. 



Carinoma, whilst generally agreeing with Cephalothrix in the situation of the lateral 

 nerve-stems, no longer retains the longitudinal medio-dorsal nerve as part of the integu- 

 ment, but in a somewhat deeper situation, enclosed in the basement-membrane. It 

 also shows very decided complications in the structure of the integument. Whereas the 

 basement layer is most closely similar to that of Carinina and Carinella, the outermost 

 integumentary layer is much more distinctly cellular, provided with unicellular glands, 

 and separated from the deeper glandular layer by the development of two layers of 

 muscular fibres that were first noticed by MTntosh (XXIV), and by him interpreted as 

 two accessory muscular layers of the body-wall. They are such, in fact, although I feel 

 confident that we may look upon them as forming an integral part of the integument, 

 and as being, together with it, wholly of epiblastic origin. Not wishing to give a figure 

 of Carinoma, which does not form part of the Challenger collection (the diagrams on 

 PI. XL may, however, be consulted) , I must needs appeal to the confidence of the reader 

 that a glance at a transverse section of the integument of Carinoma carries with it the 

 conviction that it is, in this respect, truly the most conclusive intermediate form between 

 Carinina and Eupolia, so that we are amply justified (l) in declaring the basement 

 membrane (B of PL III. figs. 3, 4, 7 ; PI. IV. fig. 1) to be not homologous with the one 



(ZOOL. CHALL. EXP. — PAST LIV. — 1887.) Hllh 8 



