NOTES. 44 1 



amount of air absorbed depends upon it. This objection is positively 

 refuted by experiment, and I have given the figures, which prove that it 

 is quite immaterial whether the surface of the water exposed to the air 

 is large or small ; and in the same way the variety of forms and sizes in 

 the vessels employed in the experiments sets aside the idea that the 

 lateral pressure could have any appreciable effect. 



Note 67, page 167. This seems to have been the case with the 

 Asellus reared by me in an hermetically closed aquarium (see p. 160). 



Note 68, page 167. In view of the obscurity which prevails on this 

 point, I think it advisable to appeal to a physiologist of acknowledged 

 repute. Paul Bert says in his Leqons sur la, Physiologie comparke de la 

 Respiration, word for word, as follows : ' La question de savoir 4 quel 

 organe il convient d'attribuer ... la fonotion respiratoire est souvent 

 d^battue avec uno insistanoe pour le moins inutile. Toute membrane 

 animale ^tant susceptible de dissoudre I'oxygfene et, par suite, de se 

 laisser traverser par lui, il est Evident que la surface exterieure du corps 

 est, tout entiftre, une surface respiratoire, et que toute surface interieure, 

 comme le tube digestif, pent et doit etre elle-meme, si le milieu oxygeufe 

 s'y introdciit, une surface respiratoire.' (' The question to which organ 

 we should attribute the function of respiration is often discussed with a 

 persistency which, to say the least, is useless. Every animal membrane 

 is capable of dissolving oxygen, consequently of being penetrated by it ; 

 so it is evident that the whole external surface of the body is a respira- 

 tory surface, and that any internal surface, as, for instance, the digestive 

 canal, can and must also be a respiratory surface, if the oxygenated 

 medium can but reach it.') We naturally designate as an ' organ of 

 respiration ' in the stricter sense, one which by its laminated or foliated 

 structure and highly developed vascular tissue appears to be specially 

 qualified for the function of respiration. 



Note 69, page 167. All animals living in water are not characterised by 

 a soft skin.— for instance, crocodiles, turtles, many snakes, the whale, 

 many insects, &c. In all these respiration is effected by vessels fitted 

 for the passage of air, by lungs in the vertebrata, and by tracheje in 

 insects. But among these last, when gills do occur, as is the case with 

 many larvas, the membrane which covers them is extremely thin, and 

 easily penetrable by the air. 



Note 10, page 171. These mantle-gills of Lucina pldlippincnsis have 

 not been hitherto described, and are figured for the first time in the 

 text. They are large tufts which form two pairs situated on the sur- 

 face of a membrane which begins at the anterior adductor and traverses 

 the pallial cavity, and which has in its posterior part a narrow slit for 

 the passage of the very long and slender foot. These tufts of mantle 

 gills are during life very large ; they contain, internally, an extremely 

 developed vascular network ; the vessels unite at the root of the gills to 

 Eorm a large trunk, which passes, without becoming confounded with 



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