FHOLADID.E. 



PHOLADID.E. 



Tab* cylindrical, straight or flexuous, closed with age at the buocal 

 extremity, ao u to envelop the animal Dd its ball ; always open t 

 toe other, and lining the cavity into which the animal ha* introduced 



U X. Hang's definition of Teredo, excluding T. gigantea (Sep- 



ten*), of which he gives the following definition, observing that it 

 eloMlj approximates to the Tmdina and Fittulana : 



Animal unknown. Shell unknown. Tube calcareoui, thick, solid, 

 in the shape of a very elongated cone, and irregularly flcxuous, fur- 

 nished intrmally with imall incomplete annuliform septa ; terminated 

 at one of iU extremities by a convexity, and at the other by two 

 deader and wparated tubes. 



The number of species of Teredo (exclusive of Septaria) recorded by 

 Lamarck in the ' Animaux ani Vertebrea ' (1818) were two, T. naralu 

 and T. paimulatui ; of the latter, Lamarck, who bad awn neither its 

 tube nor iU shell, tayi that it probaUy only differs from T. naralu 

 in iu greater ate, iU longer pal mules baring been more easily 



Hewn. Forbes and Hsnley record three as true British species 

 T. Xorrofiea, T. noroiu, T. Megotaca ; and three as doubtful T. 

 biprnmata, T. muUtolta. and T. palmulata. Woodward gives 14 as the 

 number of reo> nt species, and 25 fossil 



For our early knowledge of the nature and structure of the Teredo we 

 an indebted to three investigators, Pierre Massuet, Jean Rousset, and 

 Godfrey Sellius. The work of the last-named author was a very remark- 

 able production, and be was the first to recognise the molluscan nature of 

 this animal. The study of these animals was neglected in this country 

 till it was taken up by Sir Kverard Home. He wrote a paper entitled 

 ' Observations on the Shell of the Sea-Worm found on the Coast of 

 Sumatra, proving it to belong to a Species of Teredo, with an account 

 of the Anatomy of the Teredo Navalts.' Sir Everard remarks that 

 the internal structure and economy of Teredines were so little known, 

 and so much of what was said of them by Sellius was so vague, that 

 it became necessary to acquire an accurate knowledge of the common 

 alii, before 



Teredo 



> any adequate idea could be formed of the new 



species, which he names Teredo gigantea. 



On examining the shell of T. naralu while in the wood, Sir Kverard 

 found its external orifice very small, just large enough, in fact, to give 

 to the two small tubes. The greatest thickness observed 



was l-24th of an inch. The canal in the wood at its termination, and 

 for an inch in length, was not lined with shell, but smeared over with 

 a dirty green-coloured mucus, which was also spread upon the last- 

 formed portion of shell. According to Mr. Hatchett's analysis, the 

 shell of T. narala was perfectly similar to that of T. gigantea, being 

 devoid of pbospbaU of lime, and composed of 97 parts of carbonate 

 of lime and 3 parts of animal matter. 



While the animal was in the shell alive and undisturbed, what is 

 termed the brad was in contact with the end of the canal in the 

 wood ; but on laying the bead bare, it was drawn in for an inch iuto 

 the shell The body of the animal filled the area of the shell com- 

 pletely, but appeared much smaller when taken out, in consequence 

 of the sea-water which it contained having escaped. The largest 

 of the worms examined, which were of different length", measured 

 8 inches. Many of them were alive 24 hours after being removed 

 from their shell, and in these the heart was seen to palpitate. The 

 blood in the vetxeU going to the bead was red, as also the parts near 

 th- liver ; but this colour disappeared soon after death. 



The bead of the worm was inclosed between the two concave 

 boring shells, so that what Sir Everard calls the face was the only 

 pert exposed. These shells were united together on what is termed 

 the back part of the bead by a very strong digastric muscle, having 

 a middle tendon from which the fibres go off in a somewhat radiated 

 direction, partly for insertion into the concave surface of each shell, 

 and partly into a long semicircular process projecting from the 

 posterior part of each shell The two inclose the oesophagus and 

 other parts surrounding it. The double muscle was inclosed in a 

 smooth shining fttcia. When first exposed it was of a bright red. 



On the opposite side of the bead the shells were united by a 

 ligament from which they were readily separated ; at this part were 

 two small tooth-like processes, one from the narrow edge of each shell, 

 whmth* 



icy were joined together. 

 the middle of the expose 



From the middle of the exposed part of the bead projected a kind 

 of proboscis ; which in the living animal bad a vermicular motion : 

 its extremity was covered by a cuticle not unlike the cornea of the 

 ye. On removing this, the cavity immediately beneath it was found 

 to contain a hard brown coloured gelatinous substance, like a Florence 

 flask, who the Urge end uppermost in form. Sir Everard remarks 

 that as this probmois has no orifice, there is reason to believe that it 

 sdbem to the wood, acting as a centre-bit, while the animal is at 

 work with the bll, and thus the canal in the wood is perfectly 

 cylindrical. The month was nearly concealed by the projection of 

 the pfobosein. but, when exposed, presented a very dintinct round 

 orifice brtw. en the proboaci* and the Urge digastric muscle. 



"The body of the worm,- proceeds Sir Everard, "U inclosed in 

 on* gvoeral covering, extending from the baM of the boring shell, 

 with which it is firmly connected to the root of the two amnll tube*, 

 which appear out of the wood. It terminates in a small double fold 

 forming a cop, on the inside of which are fixed the long small stems 



of two opercula, which become broad and flat towards their other 

 extremity. These, when brought together, shut up the shell, and 

 inclose the two contracted tubes within it : not one ojierculum corres- 

 ponding to each tube, but in a transverse direction. In the T. gigantea, 

 the opercula are similarly situated, each shutting up one-half of the 

 bifurcation. At the base of this cup the general covering is thick and 

 ligameutous, for about one-fourth of an inch in length, where the 

 sterns of the opercula are connected with it ; and at one opot of this 

 thickened part there is an adhesion to the cylindrical shell, which is 

 the only part of the animal connected with it There is a depression 

 in the shell pointing out this spot The double fold of the outer 

 covering, that forms the cup, contains the sphincter muscle, which 

 closes the orifice by bringing the opercula together. The general 

 covering is composed of two membranes, the outer the strongest, and 

 made up of circular fibres, the inner much finer, having no fibrous 

 structure. On the back of the animal, this covering is firmly con- 

 nected to the parts underneath, aud is there strongest On the belly 

 it forms a cavity, and is thinner. It is everywhere sufficiently trans- 

 parent to show the different viscera through it" 



In this paper Sir E. Home examines in detail the anatomy of these 

 creatures, and left little further to be known on that point 



With regard to T. gigantea, he observes that, when arrived at it* 

 full growth, it closes up the end of ita shell, and so does T. natalit. 

 Sellius believed that the animal by this act formed its own tomb, 

 since it could no longer destroy the wood in which it was contained. 

 Sir Everard however remarks that in T. gigantea death is not a con- 

 sequence of seclusion from the substance in which it i imbedded. 

 In some of Mr. Griffith's specimens the shell was just covered in, and 

 the part close to the termination extremely thin, whilst in others it 

 was increased twenty-fold in thickness. In others again the shell had 

 not only become thick, but the animal had receded from its first 

 inclosure, and had formed a second three inches up the tube, and 

 afterwards a third two inches further on, and had made the sides 

 thicker and thicker, so as to diminish the canal in proportion to the 

 diminution of its own size. 



Animal of Teredo naralit out of the shell. 



1, the opercula are wanting, and the tubes retracted. 2, the opercula in their 

 situation, and the tubes protruded, a a, the boring-shells ; 6, the proboscis , 

 c, the mouth ; A d, the contents of the abdomen seen through the transparent 

 external covering ; e e, breathing orpins seen in the same way , ('Philosophical 

 Transactions.') 



Shell and Tube of Trrrio narala. 



a, Tubes and vlret In their position at the end ; 6, e, two views of the valves ; 

 d, double nperculnm ; e, representation of the protrusion of the two tubes of the 

 animal. ( Philosophical Transaction*.') G 1). Sowerby. 



Sir Everard considers these facts as proving that Teredo giyantea, 

 when arrived at its full growth, or whenever it is prevented from 



