Respiration in Invertebrate Animals. 407 



considerably larger * than those of the blood of the Gasteropod 

 and Cephalopod mollusks. This difference flows naturally from 

 the greater diameter which the blood-vessels of the former pre- 

 sent as compared with those of the latter. On another occasion 

 and in another place, the author will show that the same differ- 

 ences of size distinguish the blood-corpuscles of the lower Crus- 

 tacea from those of the higher. This is either the consequence 

 or the cause of the disparities of calibre in the branchial vessels 

 which occur in these two sections of the same classes. They 

 are visible facts which bear most explanatively upon not only 

 the morphic, but upon the subtler organic and chemical differ- 

 ences which mark the nutritive fluids of a less highly orga- 

 nized animal from those of another of higher standard ; for it 

 scarcely admits of doubt that the vital standard, the nutritive 

 value of any given animal fluid, bears a direct ratio to the nu- 

 merical amount of its floating corpuscles. As in the animal 

 scale followed upwards, the floating globules of the blood become 

 smaller and smaller and more and more numerous, correlatively 

 the circulating channels gradually decrease in sectional area, 

 become more and more subdivided and multiplied, until at length 

 in the higher mammals the bore of the ultimate capillary exceeds 

 little the diameter of the individual blood-corpuscle. These 

 general views will serve to impart meaning to the minute ana- 

 tomical details which are now to follow. 



The Tubulibranchiate genera, Vermetus, Dentalium, and Ma- 

 gilus, are commonly placed at the bottom of the Gasteropod 

 scale. For this disposition no reason can be drawn from the 

 position and general anatomy of the branchial cavity or from 

 the structure of the gills. M. Philippif gives a figure which the 

 author has copied (PI. XI. fig. 1), in which the organs {a & b) 

 contained in the respiratory chamber are clearly exhibited. The 

 gills (a) are as perfectly pectinated, that is, they conform in 

 figure and structure with those organs in the higher Gaste- 

 ropods which are described as ^pectinate ' gills J. They occupy 



* The measurements upon which this general statement is based will 

 be published in the next paper on the Blood in the ' British and Foreign 

 Med.-Chir. Review.' 



t Euumeratio Molluscorum Sicilia; ; and Regne Animal, ])1. 62. 



X The word ' pectinate,' as will be subsequently shown, is anything but 

 descriptive of the real figure of the branchial laminae of the Pectini- 

 branchiata. To describe them as comb-like is to suggest a vexy false com- 

 parison. If the naturalist who first coined the word had isolated a single 

 leaflet from the gill of a Peetinibranch and defined its outline, such a word 

 never could have suggested itself. The same ridiculous disparity between 

 the thing and the uame will be found to occur in other designations of 

 Orders. False titles bke these — terms indeed constructed upon imperfect 

 knowledge — illustrate the difficulty which must ever attend the attempt to 



