GENERAL REMARKS. 3 



Sclimarcla's plates, and the descriptions of other authors. Thus as regards beauty and variety 

 of colouring the Nemerteans vie with any other group in the invertebrate series ; while in 

 the silky sheen and ever-changing iridescence of the active cilia, with which their whole 

 bodies are covered, they surpass in some respects their gaily tinted superiors — the true 

 Annelids. 



The sexes of the Nermeteans do not appear to be distinguished by any peculiarity of shading, 

 except where the ova or spermatozoa are observed through the translucent tissues of the adults. 

 The reflections in regard to the bright colouring of these forms are somewhat cursorily treated by 

 Mr. Darwin in his recent work. 1 These animals, he says, like many other invertebrates, 

 " apparently stand too low in the scale for the individuals of either sex to exert any choice in 

 selecting a partner, or for the individuals of the same sex to struggle in rivalry." The Nemerteans, 

 however, are not devoid of sexual instincts, and the deposition of ova by a female, even at some 

 distance from the male, gives rise to the immediate discharge of his special secretion. Thus 

 Mr. Darwin would be furnished with the facts for stating that the best developed and most 

 forward individuals would have most chance of securing numerous and healthy progeny. Their 

 colours are not due to blood or bile, but are strictly skin-products, yet it would be as easy (or as 

 difficult) to prove them advantageous to the creature as to demonstrate that the pale blood of 

 some animals, the green or red of others, has been formed (as to colour) by natural or sexual 

 selection. Indeed, there is scarcely a limit to the range of theory on such subjects, and it is hard 

 to decide the one way or the other. The argument that the bright colours may be of use in 

 leading their enemies to recognise them as unpalatable will scarcely suit, since fishes feed readily 

 on some of the brightest. Neither can the proposition, available in the case of the soberly clad 

 blind beetles, be of service, since some of the most gorgeously tinted {e.g., Carinella annulata and 

 Linens bilineatus) are devoid of eyes ; nor are the animals coloured in any special manner so as 

 always to resemble their surroundings, as may be noticed in the olive-green and reddish varieties 

 of Linens g ess erensis. Tetrastemma Candida, on the other hand, assumes a greenish hue in certain 

 instances amongst the littoral algae, and the food of the translucent Cepltalotltrix has a wonderful 

 effect in colouring the cells of its alimentary region. Some of the most vividly tinted species 

 live in obscure crevices and creeks, where light can rarely enter. The bright reddish ova, 

 again, of Amphiporns pidcher, which shine through the pellucid integuments, must render the 

 female for a period a more conspicuous object than the male or undeveloped animal. 



Though Prof. Grube's boatman saw the head of Linens marinus ' shine/ and Viviani 

 states that Tlanaria retusa is uniformly luminous, none of the British Nemerteans show this 

 property. 



There are, so far as at present known, thirty-one species of Nemerteans inhabiting the 

 British Islands, and described in the following pages. The majority have been previously found ; 

 a few are new to Britain or to science. 



1 c rr\ 



The Descent of Man/ &c. 



