^ 196. 



THE ACEPHALA. 



213 



work of much smaller 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 difiiculties. 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-lesa 

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

 the body?'"' At all events, this portion of the oi'ganization 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 



II) has given very beautiful figures of the aquifer- 

 ous system of tlie mantle and foot of Pecten, 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 FrorieiPs 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. 



6 I have seen it thus, at least with Unio, and 

 Anodonla. 



7 Df.lle Chiaje (Descriz. &c. III. p. 53) thinks 

 that, with the Lamellibranchia, the sanguineous 

 system opens externally through special orifices. 



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 Frorieo^s neue Not. XXXVII. 

 p. 324, XXXVIU. p. 103.*" 



* [§ 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 subjea 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. 225, PI. VIII. or Silliman's 

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

 nute examination of the surface of the foot of Te- 

 redo JVorvegica 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 

 fiioe or more elevated {joints near the centre. These 



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 massi'S." This author thinks that this, aa 

 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 Hanrnck^s 

 paper in the Athenaeum No. 1086 ; also Quatre- 

 fages, Memoire sur 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 mcst probal':e 

 that this process is effected by the action of c\\vx 



