^ lOG. 



THE ACEPHALA. 



213 



■work of much sniallLU- canals is seen expanded between and above them, 

 and which can be only the blood-canals that were already visible before 

 inflation.'^* But the existence with these animals of a double system of 

 lacunae having this interpretation, is attended with many difficulties. For 

 then it must be admitted that one of these systems contains only water, and 

 the other blood ; and*it is difficult to understand how two kinds of wall-less 

 canals can traverse the body without passing into each other. But then, on 

 the other hand, if the aquiferous canals are regarded as veins, and the other 

 canals as arteries, how can this be reconciled with the fact that, in this case, 

 the blood system would open externally and the blood escape through the 

 natural orifices, while the water would be mixed with it from passing into 

 the body?^*^^ At all events, this portion of the organization of these ani- 

 mals still requires a more thorough investigation. 



CHAPTER VIII. 



ORGANS OF SECRETION. 



§ 196. 



The relations of the mantle to the secretion of the shell-substance and 

 the byssus-forming organ, have already been spoken of.^^' It now only 



11) has given very beautiful figures of the aquifer- 

 ous system of the mantle and foot of Pect fin ^ Pin- 

 na, Solen and Mactra, but has regarded it as a 

 Rete lymphatico-vasculosum.. Milne Edwards 

 (Compt. Rend. XX. p. 271, or Ann. d. Sc. Nat. III. 

 184.5, p. 300, or Froriep's neue Not. No. 733, p. 

 99), who has seen these canals in Pinna, Mactra, 

 Ostrea, &c., regarded them simply as a system of 

 lacunae common to all the Acephala. 



G I have seen it thus, at least with Unto, and 

 Anodonta. 



<■ Delle Ckiaje (Descriz. &c. III. p. 53) thinks 

 that, with the Lamellibranchia, the sanguineous 

 system opens externally through special orifices. 



* [§ 196, note 1.] The means by which the 

 Teredina penetrate the woody or stony substances 

 in which they live, have received some investiga- 

 tion of late, and I refer here to the subject from its 

 alleged anatomical relations. 



According to Hancock (Proceed. Brit. Assoc, 

 for the Advancem. of Sc. 1848, or Ann. of Nat. 

 Hist. 1848, II. p. 22.5, PI. VIII. or Silliman's 

 Amer. Jour, of Sc. 1849, VII. p. 288), " On a mi- 

 nute examination of the surface of the foot of Te- 

 redo Norvegica it is found under the microscope 

 to be crowded with minute brilliant points which, 

 on being compressed, consist of comparatively 

 large crystalline bodies imbedded within them. 

 These crystals are numerous and of various sizes 

 and shapes, chiefly five and six sided, but not by 

 any means regularly so. They all agree in having 

 one or more elevated points near the centre. These 



1 See above §§ 174, 179. According to Deshaycs, 

 Teredo has, at the anterior extremity of the body, 

 a gland concealed between the valves and which 

 communicates with the mouth of the animal. Its 

 product would serve to dissolve the wood in which 

 this animal bores. This glandular apparatus 

 which, according to Deshayes exists also with 

 other Teredina which live in calcareous matters, 

 demands a further examination ; see Comp. Rend. 

 XXII. p. 38, 300, or Froriev^s neue Not. XXXVII. 

 p. 324, XXXVIII. p. 103.* 



bodies are highly refractive, and are for the most 

 part pretty regularly distributed over the whole con- 

 vex surface of the foot, but are occasionally congre- 

 gated in masses." This author thinks that this, as 

 also all other boring Mollusks, excavate by means 

 of these parts which rasp down the substance to be 

 removed. See as corroborative of these views, Clark 

 Ann. Nat. Hist. 1850, V. p. 6. But naturalists 

 are not agreed on this point, and however it may 

 be with Teredo, yet with Pholas, other observers 

 have failed to find these rasping particles in ques- 

 tion ; see a report on the discussion of Hancock^s 

 paper m the Athenaeum No. 1086 ; also Quatre- 

 fages, Memoire but le Genre Taret, Ann. d. Sc. 

 Nat. 1849, XI. p. 33, and History of British Mol- 

 lusca by Forbes and Hanley, p. 105. 



After all, it would seem that it is most probable 

 that this process is effected by the action of cilia 



