l.AMrKEYS. 



1181 



lateral line, wliich still serves one uf the most impor- 

 tant senses possessed by fishes and batrachians. 



The lateral-line sj-stem of the Lampreys retains 

 perhaps a relic, at least a reminder, of the primitive 

 condition assumed by Beard, a pore of the system being 

 present above each gill-opening (fig. 349, Ihrs). In its 

 extension over the body this system is otherwise not 

 unlike that of the Teleosts. Behind the eyes run two 

 trans\erse series of pores (c and stp); and the lateral 

 line proper is double {I»i and /(/). The frontorostral 

 branches and their subdivisions are most distinct below 

 and before (,S'0 the eyes and in two parallel longitudinal 

 rows ((■) on the upper surface of the snout. Round the 

 lower jaw runs a mandibular branch {)ii), which sends 

 out backwards on each side a sub-branchial series (Ibri) 

 below the gill-openings. In most cases, however, all 

 these pores, except the rostral, are very difficult of 

 detection. 



Another primitive condition is manifested, accord- 

 ing to Laxgerhaxs, in the skin of the Lampreys, its 

 outer epidermal layer (cuticular cells) being frerpiently 

 furnished, though irregularly and in patches, with cilia 

 — calling to mind a very common appearance in the 

 skin of the invertebrates. But in the Lampreys, according 

 to Laxgerhass, these cilia are dead, motionless (sensory 

 hairs). Neither the Lampreys nor the following fishes 

 show any sign of squamous growths in the skin. 



The intestinal canal of the Lampreys is simple and 

 straight, the divisions being scarcely distinguishable from 

 without. Only at the extreme front and back is it attached 

 by a mesentery to the dorsal wall of the abdominal 

 cavity; throughout the rest of its course it lies free in 

 the cavity. The anterior pai-t, answering to an ceso- 

 phagus and a stomach, is wider but has thinner walls 

 than the duodenum, which is lined with longitudinal 

 folds, one of them deeper than the rest and bending at 

 the middle of the duodenum into three or more spiral 

 roils. Behind the duodenum and separated tiierefrom 

 by an annular valve, lies a short but somewhat dilated 

 rectum. The liver lies as usual in the extreme front 

 uf the abdominal cavity, and is rather small, Ijut firm 

 and without lobes. There is no gall-bladder. The air- 

 Madder is also wanting. The kidneys are paired and 

 ribbon-like, with the sharp inferior margin hanging free 

 in the posterior part of the abdominal cavity, but ex- 

 tending forward beyond the middle of its length. Their 

 efferent ducts have a common opening at the top of a 

 l)apilla projecting behind the cloacal aperture and longer 



and more pointed in the males than in the females. 

 This conunon outlet, however, has on each side (to the 

 right and left) an opening (a slit) from the abdominal 

 cavity, and by this route the sexual products, both ova 

 and sperma, after being shed into the said cavity, are 

 expelled through the papillar orifice. Both the ovaries 

 and the testes are uni)Mired, suspended between the kid- 

 neys, without special deferent canals. When ripe, they 

 fill the abdonunal cavity throughout its length, sur- 

 rounding the shrunken intestine. 



Especially interesting is the foremost part of the 

 intestinal canal, the a'sophagus, as it appears during the 

 metamorphosis of the Lampreys. In their larva?, the 

 Prides {Ammoavtes), the branchial cavity (fig. 351, 

 hr I — VII) couuuunicates directly on the one hand 

 (anteriorly) with the pharynx and mouth, on the other 

 (behind) with the (esophagus (oe.s) and the intestine, so 

 that all food must pass through the branchial cavity in 

 company with the water used for respiration. During 



Hir-— 



" ■ ' i '' 



MTM hrl 



nd 



nhr 



br VII 



Fig. 351. Section through the forepart of a Pride (Ammoccetes), 



about 3 times the nat. size. 

 abi; brauchial artery, with seven openings, for the arterial branches 

 supplied one to each gill-opening; br I — VII, first-seventh branchial 

 sacs; C, heart; Uh, notochord; Hy, nostril; La, anterior lip; Lp, 

 posterior lip; -1/, posterior (inner) mouth cavity; Ml, myelon; MT, 

 mouth tentacles; oes, lesophagus (anterior part of intestine). 



the metamorphosis, however, the posterior passage is 

 closed, and a new oesophagus (fig. 350, oes) is formed 

 above the branchial cavity, in the form of a string first 

 solid and afterwards hollow. The food receives a .special 

 passage. The water used for respiration passes neither 

 thi'ough the mouth nor the nose, but must be received 

 and expelled thi-ough the branchial apertures. At the 

 same time the rostral region is developed, from the 

 conixa traheculantm. (see above) to the jaws and denti- 

 tion inclusive. 



The family of the Lampreys hardly contains a 

 score of species, though more have been described. 

 These are distributed among four or five genera, only 

 one of which belongs to the Scandinavian fauna. 



