222 THE BLOOD. 



happened even after twelve hours had elapsed from the 

 exsection. The heart, in another experiment, being ex- 

 posed and laid naked to the eye, was observed to beat spon- 

 taneously for a few seconds, then to stop for about the 

 space of a quarter of an hour, when it again began to beat 

 quickly and violently without any obvious cause, so that 

 this learned physician thinks it certain that, in these ani- 

 mals, the motion of the heart is not beyond its control, but 

 also voluntary or subject to the will,* — an inference in 

 which you will not be disposed to coincide. In a small 

 Snail just hatched, Bradley counted about three seconds 

 between each jDulsation ; and in an old Snail from six to 

 seven seconds elapsed. f Gaspard saw the heart of a Vine- 

 yard Snail (Helix pomatia) beating, in the summer, twenty- 

 five to twenty-eight times in a minute ; and that of a Pond- 

 mussel contracted, according to PfeifFer, fifteen times in the 

 minvite.;j; On examining a specimen of Carychium lineatum 

 our mutvial friend, Mr. Alder, observed, through the trans- 

 parent shell, that its heart beat only eight times in a 

 minute, and he was about to conclude that the slowness of 

 locomotion, in this class of animals, resulted from the tardy 

 circulation of the blood, when, on examining a few speci- 

 mens of Vitrina pellucida, he was surprised to find that 

 their heart beat about a hundred and twenty times in a 

 minute ! The latter was in a state of action, and the former 

 of rest. He has since found, that the number of pulsations 

 in the same individual is very unequal at different times, — a 

 variableness dependent on external influences, doubtless, 

 and principally, perhaps, on the temperature of the air or 

 water to which the animals are exposed. § 



The blood itself is of a bluish-white colour, and glutin- 

 ous consistence. 1 1 Lister tells us, that when he kept the 



* Exer. Anat. de Coch. p. 38. Excr, Anat. tert. p. 13. 



t Phil. Ac. of the Works of Nature, p. 129. 



j Tiedeniann's Comp. Phys. i. 156. 



§ Mr. Garner states that in the Laniellibranchiata the pulsations of the 

 heart are generally from twenty to thirty in the minute. — C/iarlesw. Mag. 

 N. HistAii. 168. Messrs. Alder & Hancock have given the number of pul- 

 sations in the following Nudibranchiata : 



Polycera ocellata 72 — 88 Ancula cristata 72 — 75 



Doto coronata 60 Polycera lessonii 62 



Eolis coronata 65 Hermsea dendritica 96 



Eolis papillosa 50 



II Sir E. Home says that the blood of the Teredines is red, Comp. Aiiat. 

 i. 32; and that of the Planorbis is almost purple. — Milne-Edwakds, Elem. 

 de Zool. p. 18. Milne-Edwards has found, in the neighbourhood of Pa- 

 lermo, an Ascidia with red blood. — Ann. and Mag. N. Hist. xv. 69. 



