^^Wip 



VOL. LXXV.] PHILOSOPHICAL TRANSACTIONS. $. 



testine at the posterior end opens externally, forming the anus. From the con- 

 tracted state of the animal, the intestine is thrown into a number of folds. 



On examining the cones and the tentacula, Mr. H. at first believed that the 

 spiral form arose from their being in a contracted state ; and that when the. 

 tentacula were erected, the cone untwisted, forming a longer cone with the ten- 

 tacula arising from its sides, like the plume from the stem of a feather ; and 

 that this stem was drawn in or shortened by means of a muscle passing along 

 the centre, which threw the tentacula into a spiral line, similar to the penis of 

 many birds ; but how far this is really the case, he was not able to ascertain. 

 The internal structure of this animal, like most of those which have tentacula, 

 is very simple ; it differs however materially from many, in having an anus, most 

 animals of this tribe, as the Polypi, having only one opening, by which the food 

 is received, and the excrementitious part of it also afterwards thrown out ; this 

 we must have supposed, from analogy, to take place in the animal which is here 

 described, more particularly since it is inclosed in a hard shell, at the bottom of 

 which there appears to be no outlet ; but as there is an anus this cannot be the 

 case. 



It is very singular, that in the leach, polypi, &c. where no apparent inconve- 

 nience can arise from having an anus, there is not one, while in this animal, 

 where it would seem to be attended with many, we find one ; but there being 

 no anus in the leach, polypi, &c. may depend on some circumstance in the 

 animal economy which we are at present not fully acquainted with. Tiie uni- 

 valves, whose bodies are under similar circumstances respecting the shell with 

 this animal, have the intestine reflected back, and the anus, by that means, 

 brought near to the external opening of the shell, the more readily to discharge 

 the excrement ; and though this structure, in these animals, appears to be solely 

 intended to answer that purpose, yet when we find the same structure in the 

 black snail, which has no shell, this reasoning will not wholly apply, and we 

 must refer it to some other intention in the animal economy. In this animal 

 we must therefore rest satisfied that the disadvantageous situation of the anus, 

 with respect to the excrement's being discharged from the shell, answers some 

 purpose in the economy of the animal, which more than counter-balances the 

 inconveniences produced by it. It would appear, from considering all the cir- 

 cumstances, that the excrement thrown out at the anus must pass from the tail 

 along the inside of the tube, between it and the body of the animal, till it comes 

 to the external opening of the shell, as there is no other evident mode of dis- 

 charging it. 



How the tube or shell is formed in stone or coral is not easily ascertained. It 

 may be asked, whether this animal has the power of boring backwards as the 

 Teredo Navalis probably does, or whether the stone or coral is formed at the 



