1-212 



SCANDINAVIAN KISllKS. 



form tl 

 slightly 



Here ill J!)(iii(h}<isf<))iia tlierc is iiardly any such ^ Jlniiicl/in.stonia, is th;it ihc iiotochi.ird (ti^'. 060, Ch) 

 r: — tlie spinal cord is a string of almost uni- projects forward beyond tlie anterior end of tlie spina! 

 lickness, gradually ta])ering backwards, and only : cord (il///) and in front of tlie mouth ajierture (/ and f/). 

 dihited at its anterior end (fig. ?.6(), «) so as At the ])osterior end of the body tlie case is different. 



Thei'c (tig. :'>i\7) we find an u])curved dilatation of 

 the medullispinal canal («), reminding us of Myx'nic 

 (fig. ?,'A). 



The mouth is of a curious structure for a verteb- 

 rate. It is neither a prehensory nor a suctorial mouth; 

 it is, so to say, merely a deglutitory mouth, edged 

 with a ring of small cartilages (fig. SB-'), / ), in texture 

 resembling the notochord. Each one of these cartilages 

 gives out a jjrocess (r/) to form a sup|)ort in one of 

 the so-called cirri which sujTound the oral aperture 



Fig. 366. Anterior end of tlie spinal cord and tlie nerves thereof in 

 Branchiostonm lanceolatum, seen from above and magnified. After 



VoGT and YuNG. 



a. medullispinal swelling and its cavity; //, first, c, second pair of 



nerves; rf, pigment spot (eye spot?); e, third and fourth pairs of 



upper (posterior, sensory) nerves; /, spin.il cord. 



Fig. 367. Caudal end of linnic/aostoina Iniiccotntntn, seen from the 



left and magniticd. After VoGT and Ylxg. 



a, sjiinal curd: li, notochord; c, upper ramifications of the sensorj' 



nerves; (/, lower ramifications of the same; e, hindmost myoeonima 



(boundary of the hindmost myomere). 



to form a kind of cerebral vesicle. And the notochord 

 tapers to a pointed termination at each end of the body. 

 A peculiarity never seen in any vertebrate higher than 



Fig. 368. Posterior wall of the mouth cavity (postoral sphincter or 

 reliim) with its twelve centripetally meeting cirri, which are funnshed 

 with the sensory bodies first described by Langerhanr, bundles of 

 sense-hairs on thickened parts of the eiiithelium. After H.\Y LANKESTliK. 



outside, but are folded inwards wiien the mouth is 

 closed. These cirri are almost exactly similar to the 

 sense-filaments or tentacles possessed liy many of the 

 lower animals. At their base they are united to a 

 membrane coursed by muscular fibres; and their sur- 

 face is clotlied witli a cylindrical epitiielium, among 

 whose cells some are ciliated, others prolongated out- 

 wards into stiff setip, ^vhich are collected in verruciform 

 bundles, and connected inwards witii nerve fibrillae, 

 whence tiiey iiave been inter] ireted as organs of taste. 

 \\'itliiii the mouth is a buccal (pliaryngeal) cavity, 

 the inner surface of which displays active ciliary mo- 

 tion, especially along the margins of a number of 



