929 



GASTRIC JUICE. 



GASTROCH^ENA. 



930 



great variation, not only in the number of lateral plates, but in several 

 other less obvious respects. The former may occasionally be found of 

 every intermediate number between that which characterises the 

 G. leiurui, Cuv., and that which appears in the G. trachurus of the 

 same author. This number moreover is sometimes found constant 

 in specimens which differ remarkably in other respects ; at other times 

 varying, when all other characters remain the same. From these 

 circumstances combined, I feel satisfied that the above are mere 

 varieties, notwithstanding the high authorities on which they stand 

 recorded as distinct species." (' Manual of British Vertebrate 

 Animals,' p. 349.) 



A writer in th 'Magazine of Natural History,' vol. iii. p. 329, 

 relates some interesting observations illustrative of the habits of these 

 little fishes whilst in confinement in a tub. " When a few are first 

 turned in, they swim about in a shoal, apparently exploring their new 

 habitation. Suddenly one will take possession of a particular corner 

 of the tub, or, as it will sometimes happen, of the bottom, and will 

 instantly commence an attack upon his companions ; and if any one 

 of them ventures to oppose his sway, a regular and most furious 

 battle ensues ; the two combatants swim round and round each other 

 with the greatest rapidity, biting and endeavouring to pierce each other 

 with, their spines, which on these occasions are projected. I have 

 witnessed a battle of this sort which lasted several minutes before 

 either would give way ; and when one does submit, imagination can 

 hardly conceive the vindictive fury of the conqueror, who, in the 

 most persevering and unrelenting way, chases his rival from one part 

 of the tub to another, until fairly exhausted with fatigue. They also 

 us their spines with such fatal effect, that, incredible as it may appear, 

 I have seen one during a battle absolutely rip his opponent quite open, 

 so that he sank to the bottom and died. I have occasionally known 

 three or four parts of the tub taken possession of by as many other 

 little tyrants, who guard their territories with the strictest vigilance ; 

 and the slightest invasion invariably brings on a battle. These are 

 the habits of the male fish alone ; the females are quite pacific ; 

 appear fat, as if full of roe ; never assume the brilliant colours of the 

 male, by whom, as far as I have observed, they are unmolested." 



Dr. James Stark discovered uoarj Edinburgh a new species of the 

 present genus, which greatly resembles the common species, but is 

 rather smaller, and has four spines on the back. It is the G. fpinulosus 

 (Four-Spined Stickleback) of Yarrell and Jenyns. 



A still smaller species the Ten-Spined Stickleback (G. pnngitim, 

 Linn.) is distinguished, as its English name implies, by the possession 

 of ten spines on the back, and these are short and of equal length. 



This, as well as the other species of the genus, is occasionally found 

 in the salt-water. It appears to be pretty generally distributed 

 throughout England. 



Lastly may be noticed the Fifteen-Spined Stickleback (G. spinachia, 

 Linn.), which is also found in England, a comparatively large species, 

 being 5 or 6 inches in length, of an elongated and slender form, and 

 having the snout much produced. The fifteen spinea on the back are 

 small and short ; the fins are proportionally large. 



This species appears to be confined to the salt-water, and feeds upon 

 small Crustacea, as well as the eggs and fry of other fishes. It 

 constitutes the sub-genus Spinachia, and is the Spinachia vulgaris of 

 Fleming. 



GASTRIC JUICE or ACID. [DIGESTION.] 



GASTROBRANCHUS. [PETROMYZID*;.] 



GASTROCH^E'NA, a genus of Acephalous Mollusca belonging to 

 the order LameUibranchiata. It was established by Spengler. Lamarck 

 places it between Pliolai and Solen, and Cuvier between Fistulana and 

 Teredina. M. Deshayes, in his edition of the ' Animaux sans Vertebres,' 

 ays that it is evident that Lamarck came to very erroneous conclu- 

 sions as to this genus. The animal, observes M. Deshayes, has two 

 posterior very short siphons when it is contracted ; the lobes of the 

 mantle are united up to the gape of the valves and even a little higher; 

 this gaping of the valves as well as the divarication of the lobes of the 

 mantle, gives passage to a great short cylindrical foot, like that of the 

 Pholade* ; but this opening is not at all destined for the passage of 

 the siphons, as Lamarck supposed. 



Mr. G. B. Sowerby (' Genera of Recent and Fossil Shells') remarks, 

 that the genera Pholat, Mya, Mytilus, and Chama, have by turns 

 served as a receptacle of the shells of this genus. He observes that 

 Lamarck has adopted Spengler's name, but has placed it next to 

 Pholat, apparently not having known that the animal forms its own 

 testaceous tube, either as a lining to the hollow it has previously per- 

 forated, or as a covering for its shell in those instances in which it 

 has not perforated at all, but in which it has taken up its abode, as it 

 frequently does, within some spiral univalve. Mr. Sowerby is further 

 of opinion, that the fact of the shell being inclosed in a testaceous 

 tube of its own depositing, renders it proper to remove it into 

 Lamarck's family of Tubicola, to which indeed it appears to Mr. 

 Sowerby to be more nearly related, though he notices a very consi- 

 derable analogy between the shelly tube of Lamarck's Tubicolie, and 

 the coriaceous epidermis, which not only in a great measure covers 

 the shell, but also incloses the tubes of the animal of Lamarck's 

 Pholadacerf, and Mr. Sowerby consequently thinks that the two 

 families might very properly be united. 



Professor Owen, in his paper on Clavagella, remarks how closely that 

 WAT. HIST. DIV. voi,. n. 



form follows the modifications which have been observed in Gastro- 

 chcena. [CLAVAGELLA.] 



Cuvier says that it appears that the Gastrochcence constantly have a 

 calcareous tube, and quotes Dr. Turton, M. Deshayes, and M. Audouin, 

 as having observed it. 



M. Rang says that all the Gaslrochcena; have not a calcareous tube, 

 though all of them burrow in stones after the manner of Pholades. 

 If this is to be taken literally, it does not exactly accord with the fact ; 

 for sometimes the animal does not burrow at all, at others (and very 

 frequently) it burrows in madrepores. M. Rang adds that two of the 

 species which belonged to the genus Fiatulana of Lamarck are now 

 arranged in this, and that this arrangement is due to M. de Blainville. 

 These two species, he says, are Fistulana clava aud F. ampullaria. 

 Of these, Fistulana clava is referred among the synonyms to Gastro- 

 chcena by Lamarck, and Fistulana ampullaria is declared by M. Des- 

 hayes to be a true Fistulana, but remarkable in this, that, according 

 to circumstances, it forms a free tube sunk in the sand, or perforates 

 calcareous bodies, and its tube serves as a lining to the cavity which 

 it inhabits ; this species therefore, he observes, would belong to the 

 Fiatulana; in the first case, and to the genus Gastrochcena in the second, 

 if indeed that genus be preserved. 



M. Rang states that M. Charles Des Moulins, who a long time ago, 

 and before the observations made upon this subject, had discovered 

 the existence of a tube in the Gastrochcence, had shown him this tube, 

 not only in the living species on the French coast, but in the fossil at 

 Merignac. Following De Blainville, M. Rang would divide the genus 

 Gastrochcena into the two following groups : 



a. Species whose shell is smooth and without a distinct tube, 



Example, Gastrochcena cwneiformis, &c. 



$. Species whose shell is striated from the umbo to the 



base, and contained in a distinct tube. 



Example, Gastrochcena clava. 



M. de Blainville states that the animal of Gastrochcena has evidently 

 the greatest relationship to that of Saxicava ; but as it is not entirely 

 contained in its shell, it often supplies the deficiency by forming an 

 artificial tube adhering to the walls of the cavity which it inhabits in 

 calcareous stones. 



This tube, in the opinion of M. de Blainville, offers only an acci- 

 dental character, and would thus make of species, or even of individuals 

 which are provided with it, Fistulana of Lamarck. Thus, he observes, 

 M. Deshayes has proposed to suppress the genus Gastrochcena, but he 

 would consider it more convenient not to admit the genus Fistulana ; 

 first, because it is founded upon the presence of a tube ; and secondly, 

 because it was established some time after Gastrochcena. He would 

 however prefer its restriction as he has restricted it in his ' Malacologie.' 

 In uniting the species characterised by the true shell, whether it have 

 an external tube or not, there exist already, he remarks, many species 

 of known Gastrochcence, both living in the seas of warm climates and 

 fossil in his country. M. Defrance, he states, nevertheless quotes 

 one fossil species only at Grignon, and an analogue ; and he concludes 

 by observing that Gastrochcena clava would perhaps, if it were better 

 known, form a small, distinct genus, 



Mr. G. B. Sowerby ('Zool. Proc.,' 1834) describes five new species 

 brought home by Mr. Cuming from South America and the Gallapagoa 

 Islands and Lord Hood's Islands, 



The following is M. Rang's definition of the genus : 



Animal oval, having the mantle closed with a very small anterior 

 rounded opening for the passage of a small, conical, or linguiform 

 foot : the tubes elongated and united throughout. 



Shell delicate, oblique, oval, cuneiform, equivalve, very inequilateral, 

 gaping extremely at its antero-inferior part ; umbones well marked ; 

 hinge straight and linear, without teeth ; an apophysis often showing 

 itself below the hinge in the interior of each valve ; ligament external ; 

 muscular impressions distinct, connected by a slightly marked pallial 

 impression excavated posteriorly. 



Sometimes a calcareous tube, ampulliform, short, with a rounded 

 aperture, enveloping the shell and lining the cavity of the stone. 



G. modiolina has been found on the English and Irish coasts. It 

 is a common inhabitant of the Mediterranean. 



Messrs. Forbes and Hanley adopt Gastrochcena as the type of a 

 family, Gastrochcenidce, in which they include with M. Deshayes not 

 only the genera Aspergillum, Clavagella, and Gattrochcena, but also 

 Saxicava; and express the opinion that Pelricola, and probably 

 Venerupis, have strong claims to a similar position. The following is 

 the definition given of this family in Forbes and Hanley's ' British 

 Mollusca ' : 



"The animals of this aniily are oblong or claviform, and often 

 provided with very long siphons, united almost to their extremities, 

 where their orifices are ornamented with cirrhi. The mantle is closed 

 in front, except a small opening for the passage of a very small 

 digitiform foot, very different from that of the Pholas tribe. The 

 margin of the mantle around this opening is plain. The shell is 

 equivalve, and often gaping, with valves often very inequilateral, 

 united by a simple rudiment, or in some cases a toothed hinge, often 

 variable, even in the species of a single genus. They have no spoon- 

 shaped apophysis under the beaks, nor accessory plates behind them. 

 A calcareous tube sometimes protects the valves, and in certain genera 



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