APPENDIX. 287 



exact, for they are not produced from, nor in organic connexion with 

 the ahmentary canal, as is manifest from their remaining unaifected 

 during the motions of the latter, which moreover may be removed 

 entirely from the body without bringing with it, or tearing away, 

 the presumed caeca. These are always full of some opake matter in 

 the Nemertes, and some observations lead me to believe that it varies, 

 in intensity at least, according to the nature of the animal's food, 

 whence I conclude they belong chiefly to the digestive system ; while 

 the ova appear to be developed in their interstices, and in the space 

 between them and the skin (PL II. A. fig. 2). But in Borlasia 

 the caeca are more distinctly vesicular and isolated, and although the 

 depth of colour of their contents varies also, yet they are usually 

 clearer and paler than the surrounding parenchyma, or as it were 

 empty ; and I have plainly seen in them, not often, indeed, oviform 

 bodies, which again have not been detected in the interstices 

 (PI. II. B. fig. 3). We seem, then, to have combined in them a 

 duplicity of function, — they are both nutrient and uterine cells ; 

 but how far this view can be admitted, I must leave to the determi- 

 nation of some better observer*. 



Many specimens, and several species, had been examined before a 

 trace of a nervous system could be detected, and I was ready to con- 

 clude that these worms were truly acritous, when I was prevented 

 falling into this error by the discovery of it in the Nemertes octocu- 

 lata. In this species the nervous system is distinct, and I have been 

 able since to see it in several others more obscurely. It consists of 

 a single oblong or ovate ganglion laid over and above the oesophagus 

 posterior to the heart ; and from this ganglion nervous threads 

 radiate in every direction, which are unbranched, of nearly equal 

 sizes, and soon lost in the body (PI. II. B. fig. 2). The system 

 has obviously a nearer relation to that of some of the lower Mollus- 

 cans than to any of the typical Annelidans, a fact which, however, is 

 not anomalous, for Prof. Owen has made the same remark in refer- 

 ence to some intestinal worms f. 



The circulating system appears to be complete, though very sim- 

 ple. Immediately behind the eyes there may be observed a roundish 

 spot on each side of a reddish colour, indicating the position and 

 figure of organs which are perhaps the centres of this system J. 

 These organs are connected by a cross vessel ; and from their inferior 

 aspects a fine vessel departs, which, running along each side between 



and into Kirby's Bridgewater Treatise, pi. 1 B. f. 4. The comparison may be nse- 

 fuUy extended to the Annelides, Cyclop, of Anat. and Phvs. i. 169. f. 70 ; Roget, 

 Bridgew. Treat, ii. 103. f. 200 ; and to the Tamice, ibid. ii". 83. f. 247. 



* Since this was written, farther observations have almost satisfied me that 

 the apparent differences in the formation of the caeca in these subgenera are de- 

 pendent, in a great measure, on the state of the worm in regard to repletion, — 

 the distinct vesicle-like spaces being formed by the extension and coalescence of 

 the caeca around a space filled with ova, which would seem therefore to be always 

 exterior to the caeca. 



t Proceedings of the Zool. Soc. of London, pt. iii. p. 28 ; and Trans, of the 

 Zool. Soc. i. 328-9. 



X Duges appears to have been of the same opinion. Ann. cit. p. 75. Williams 

 takes our view of the functions of these organs: see Rep. 1851, p. 189. 



