392 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



disseverance. The formation of a complete individual, and the prolonged reten- 

 tion of certain functions by the headless fragments, under circumstances so 

 adverse as the above, may give us some idea of the powers of regeneration and 

 vitality possessed by these worms in their native haunts. 



Mr H. Goodsir criticises M. de Quatrefages' description of the nervous 

 system in Serpentaria and Nemertes, and denies its existence altogether, averring 

 that microscopically the so-called nerve-trunks showed no nervous elements at 

 all, but were the testicles of the worms. I fear, however, this worthy naturalist 

 depended rather upon analogy than actual observation in this case. He accounts 

 for the nervous fibres seen by Rathke* (the first who correctly described the 

 Borlasian ganglia) passing out from the cerebral ganglia to the narrow furrows 

 on each side of the head, by supposing them to be seminal tubes on their way to 

 the furrows (his seminal apertures). M. de Quatrefages confined his examina- 

 tions chiefly to Ommatoplean ganglia. Frey and Leuckart,! again, confound the 

 cephalic sacs with the posterior part of the ganglia. M. Van BenedenJ makes a 

 curious remark in regard to his Nemertes Quatrefagii — viz., that the " collier 

 oesophagien" is peculiar for its red colour, which hue, he says, is less marked in 

 the other species of Nemertes. This colour, he explains, is not due, as believed 

 for a long time, to the nerve-ganglia, but to the vessels which surround them, 

 and it can easily be understood how the ganglia were confounded with the nerve- 

 trunks. Nothing akin to this has ever come under my observation, and the 

 minute anatomy of the region is adverse to the view. M. Grube§ had previously 

 made the same remark in describing Nemertes purpurea, Johnst., a species which 

 (judging from the descriptions) seems to differ very materially from Omma- 

 toj)lea purpurea, and is apparently a Borlasian form, but I have not as yet seen 

 any British representative. Prof. Keferstein is scarcely accurate in affirming that 

 the ganglia in this group are larger than those of the Ommatopleans. In his 

 figure of the parts viewed from the dorsum (Taf. vii. fig. 1), the cephalic sacs are 

 not discriminated. 



Lateral Fissures. — On each side of the head in Borlasia is situated an exten- 

 sive fissure (Plate X. fig. 1, and Plate XII. fig. 2, b), which commences as a 

 shallow groove at the anterior border of the snout, and terminates, as a reddish 

 pit, somewhat abruptly, just beyond the entrance to the cephalic sac. A distinct 

 narrowing of the anterior region occurs behind the fissures in B. olivacea, thus 

 marking off the cephalic boundary. There is nothing special in the anatomy of 

 these fissures, for they are formed by a simple extension of the cutaneous ele- 

 ments superiorly and inferiorly, as represented in the transverse section (Plate 

 XII. fig. 2). Their entire surface is covered with very active cilia, which, as before 

 mentioned, I have often seen cease abruptly, and again begin to play vigorously. 



* Neueste Schriften, &c. f Beitrage zur Kenntniss wirb. Tliiere, p. 73, taf. i. fig. 15. 



X Op. cit. p. 16. § Archiv fur Naturges. 1855, p. 150. 



