Respiration in Invertebrate Animals. 243 



but these are all that have come under my observation *." In 

 each of these " modifications " one common character is said to 

 prevail — the vessels reticulate — in the first only " slightly," in 

 the others more " minutely." Such is the structural law of the 

 branchiae of the Lameliibranchiates as expounded by Mr. Han- 

 cock. It is at direct variance with the prevalent and accepted 

 definition. Dr. Sharpey says — " Each gill (of Mytilus) or leaf 

 consists of two layers, which are made up of vessels set very close 

 to one another like the teeth of a comb or like parallel bars, 

 &c.f " " These bars are connected laterally with the adjacent 

 ones of the same layer at short intervals by round projections on 

 their sides," &c.J 



Here this accurate observer conspicuously indicates the differ- 

 ence between the solid projections interposed between the vas- 

 cular bands, tying them together into a horizontal lamina, and 

 the " transverse plicae " of Mr. Hancock, which transform a 

 matchless system of parallel bars into one of " minute reticula- 

 tion" (Hancock), which neither the eye nor the understanding can 

 unravel. M. Deshayes § stands in this anomalous position: — 

 he has figured accurately what he has interpreted wrongly. Albeit 

 to this author merit is due. He has pointed out clearly by the 

 pencil — what really exists in nature ; what he himself misunder- 

 stood ; what neither Dr. Sharpey nor Mr. Hancock seem at any 

 time to have recognized — a structure without which the gill of 

 the Lamellibranch could not architecturally be what it is ; a mar- 

 vellously woven fabric, refined in the utmost degree in its me- 

 chanism, adapted with incomparable skill to the purpose in view 

 — a structure which no observer either anterior or posterior to 

 the time of M. Deshayes has even suspected to exist — that ap- 

 paratus of transverse scaffolding (PI. VI. fig. 1 c, c, d) situated 

 between the lamella? of the gill, crossing at right angles the axes 

 of the interlamellar water-tubes, j,j (of the existence of which 

 M. Deshayes had not the slightest knowledge), and doubtfully 

 described by him as the true blood-channels of the branchiae ! 

 M. Deshayes mistook the laminae formed by the real branchial 

 vessels for " membranous layers or laminae, within the substance 

 of which the branchial vessels are arranged with great regularity." 

 His eye caught with correctness nearly all the parts of this 

 exquisite apparatus ; his reasoning then enveloped them in 



* Annals and Magazine of Natural History for April 1853. 



t Art. " Cilia," Cyclop, of Anat. ami Phys. 



X This concise description is rendered still clearer by the original figures 

 which accompany the famed article of Dr. Sharpey, to which I have ad- 

 verted in the text. 



§ See art. " Conchifera," Cvclop. of Anat. and Phys. 



16* 



