13 



KNOWLEDGE. 



[Jaxuary 1, 1895. 



the name of Amphioxus, and was the first to recog- 

 nize the existence of a cartilaginous vertebral column, 

 or notocbord. Tbe muscles of the body are divided into a 

 number of septa, and a rin.c; of tentacles surrounds the 

 margins of tbe mouth, while tbe notocbord is overlain by 

 the nerve-tube. The extension of the notocbord beyond the 

 anterior extremity of the latter is a very exceptional condi- 

 tion, and has suggested tbe name of Cepbalocorda for the 

 ordinal group of which the laneelet is the sole repre- 

 sentative. The atrium, or atrial chamber, is a cavity 

 surrounding most of the internal organs, and opening 

 by a relatively large aperture in tbe middle line of the 

 body. The absence of paired fins in the laneelet is 

 an important feature, as is the presence of a dorsal fin 

 running the whole length of the back, curving forwards in 

 front to join the ring of tentacles round tbe mouth, and 

 expanded posteriorly into a caudal fin. 



As regards the habits of this extraordinary creature, the 

 author writes that " in consequence of tbe extension of tbe 

 firm, and at the same time elastic, notocbord to the t'p of 

 the snout, Amphiiunix possesses an extraordinary capacity 

 for burrowing in the sand of the sea-shore or sea-bottom. 

 If an individual be dropped from tbe hand on to a mound 

 of wet sand which has just been dredged out of the water, 

 it will burrow its way to the lowest depth of the sand-hillock 

 in the twinkling of an eye. Its usual modus virmdi is to bury 

 the whole of its body in the sand, leaving only tbe mouth with 

 tbe expanded buccal cirrhi (tentacles) protruding. When 

 obtained in this position in a glass jar, a constant inflowing 

 current of water, in which food-particles are involved, 

 can be observed in the neighbourhood of tbe upstanding 

 mouths. The food consists almost entirely of microscopic 

 plants (diatoms, desmids, &c.) and vegetable (libiis. 

 While passing through tbe pharynx, the food becomes 

 involved in the slimy secretion of a gland at the base of 

 the pharynx, and is thus held in tbe pbar3'nx while the 

 water with which it entered flows out through the gill- 

 sUts into the atrial chamber. The food is then carried 

 through the intestine enveloped in a continuous cord of 

 slime or mucus, which is kept in perpetual motion by 

 the action of the cilia with which the epithelium of the 

 alimentary canal is richly provided. Occasionally it 

 emerges from its favourite position in the sand, and after 

 swimming about for some time it will sink to the bottom, 

 and then recline for a longer or shorter period upon its 

 side on the surface of the sand. When resting on the 

 sand it is unable to maintain its equilibrium in the same 

 position, as an ordinary fish would do, but topples over on 

 its side, indift'erently to the right or left." This incapacity 

 is due to the absence of the semicircular canals of the 

 ear, which regulate the equilibrium in fishes. It may be 

 further observed that the laneelet is a completely passive 

 feeder, doing nothing in the way of biting, or even sucking, 

 but merely taking what may happen to enter its mouth 

 with the inflowing current of water. 



As regards its distribution, tbe author observes that, 

 speaking generally, " the laneelet is an inhabitant of 

 shallow water ; it is essentially a littoral form, and is apt 

 to occur in the neighbourhood of any sandy shore. Its 

 occurrence, however, is often curiously local, as shown by 

 its behaviour at ^Messina. ... In the Gulf of Naples 

 it is extremely abundant ; while in Plymouth Sound, in 

 the English Channel^ it is comparatively rare. On the 

 coast of France it is said to grow to an unusually large 

 size. It has been taken in greater or less numbers from 

 many other localities in Europe, on the Atlantic and 

 Pacific shores of North and South America, and from the 

 shores of Australia, .Japan, and Ceylon. Its geographical 

 distribution may, therefore, be said to be pre-eminently 



world-wide, and, in fact, it is liable to turn up on any shore 

 in the temperate and tropical regions." 



In spite of this wide geographical distribution, all the 

 lancelets, of which there are some nine species, are 

 remarkably like one another, and form but a single geims. 

 Whether this similarity is evidence of the archaic nature 

 of these creatures (as the author considers to be the case) 

 may be doubtful ; but that the lancelets are an extremely 

 ancient type may be considered certain. That the laneelet 

 is not a fish is indisputable ; and the two main questions 

 connected with it and the other members of the Protochor- 

 data are : firstly, whether they are more closely connected 

 with the vertebrates or the invertebrates ; and, secondly, 

 whether they are simple or degraded types. 



As regards the first question, tbe fact that both lancelets, 

 ascidians, Btihinciilossus, and Ceiihalodisctis show the essen- 

 tially vertebrate character of a dorsally-situated nervous 

 system, a notocbord, and gill-slits, indicates clearly that all 

 are nearer to the vertebrates than to the invertebrates, and 

 consequently, that they cannot be regarded as direct connec- 

 ting links between the two. Nevertheless, there are not 

 wanting some signs of connection between the chordate and 

 non-cbordate types ; the peculiar larva [Taniaria) of Balnno- 

 (/lossiis having marked resemblances to tbe larvse of the 

 echiuoderms ; while in the nemertine worms the proboscis 

 exhibits certain structural approximations to that of 

 Balinwrilosaux, which contains the notocbord. And here it 

 may be remarked, as a very curious circumstance that, 

 while in the latter the notocbord persists in the anteriorly 

 placed proboscis, in the larva of the ascidians it remains 

 in tbe tail. 



On the subject of tbe degeneration, or otherwise, of the 

 existing Protochordates, the author (probably wisely) does 

 not pronounce any very decided opinion ; but tbe feature 

 last mentioned seems to indicate pretty clearly that, while 

 we may look upon these creatures to a certain extent as 

 retaining simple archaic features, yet that degeneration 

 has played no inconsiderable part in producing their 

 present structure. All that the author can suggest as to 

 the proximate ancestor of the vertebrates is, that it was 

 probably a free -swimming marine animal intermediate in 

 organization between the larva of an ascidian and the 

 laneelet. 



In a work so admirably thought out and executed as is 

 the one before us, there is but little room for criticism ; 

 and we, therefore, need only conclude by saying that 

 "Amphioxus and the Ancestry of the Vertebrates " will long 

 remain the single authority on a most interesting and at 

 the same time a most difficult subject. While fall of 

 technical details, it is so clearly expressed as to be readable 

 by all acquainted with the rudiments of zoology. — E. L. 



BOOKS RECEIVED. 



Ethics of Lileraiure. By John A. Kersey. (E. L. Goldthwait 

 & Co., Marion, Ind.) 



Cloudlaml ; A Study of the Structure ami Character <f Cluiii/.s. 

 By Eev. W. Clement Ley, M.A., F.R.Met See., with numorous 

 coloured plates, pliotographs, charts and diagrams. (Edward Stanford, 

 Charing Gross, 8.W.) 7s. 6d. net. 



Jleteoroloc/i/, Practical and Applied. Bv J. W. Moore, B.A., M. D., 

 F.R.O.P.I. (F. J. Eebman.) 8s. 



Allen's Naturalist's Lihrary : MonVeys, Tol'. 1 and 2. Bv Henrv 

 O Forbes, LLD. 6s. each. Also ButterlHes. Vol. 1. Bv W. F". Kirbf. 

 (W. H. Allen & Co.) 6s. 



Elements of Astronotnij, trith numerous examples and examination 

 papers. By George W. Parker, M.A. (Longmans, Green & Co.) 

 .5s. net. 



The Coal Question and the true value of the fuel Economizer. By 

 James O. Calvert. (6, St. Mary's Gate, Manchester.) 



