114 Ailscb Craig and its Birds. 



Explanation op Plate. — Fig. 1. — Plan of the circulation; 

 tlie arrows indicating the direction of the currents ; 11, the 

 lungs ; pp, the pericardial gland ; s, the sinus ; h, the, heart ; 

 a, the aorta ; aaaa, the various arterial branches ; i, the diges- 

 tive canal ; Ivlv, the great lateral veins ; vvvv, their branches. 

 Fig. 2. — Inner surface of the membrane of the lung, showing 

 the network of blood-vessels. Fig. 3. — Blood corpuscles ; a, 

 opaque and granular; h, with projecting processes ; c, the 

 nucleus faintly seen; d } the nucleus distinctly seen. Fig. 4. — 

 The heart and sinus, surrounded by the pericardial gland. 

 Fig. 5. — Imaginary longitudinal section in the vertical plane 

 of the animal ; h, the head ; a, the abdomen ; c, the cavity 

 which contains the heart, sinus, gland, and shell. Fig. 6. — 

 Imaginary vertical section in the transverse plane; 11, the 

 lungs ; sb, the shell-bag ; p, the pericardium ; h, the heart ; 

 pg, the pericardial gland. Fig. 7. — Plan of the pulmonary 

 organ ; 11, the lung sac of each side ; pp, the passages of inter- 

 communication ; i, the isolated patch, containing the heart, 

 sinus, shell-bag, etc., etc. 



AILSA CRAIG AND ITS BIEDS. 



Secretary to the Natural History Society of Glasgow. 



It is hardly necessary to dwell upon the general features of 

 this remarkable rock, for, like other isolated rocks of the same 

 character, it presents scenes which have often been described — 

 steep precipices towering on all sides ; high ranges of fractured 

 pillars, sometimes overhanging and shadowing the deep ; cliff 

 Beaming to rise above cliff, their massive walls streaked with 

 endless rows of soldierly sen-fowl ; tho whole island, from its 

 Bolitary position, rifling upon the view in " unattended majesty," 

 and impressing the beholder with a feeling of awe. 



When ncning it in calm weather no one can fail to be 

 struck by tli<' grandeur of its precipitous dill's, reaching 1200 

 feel above the sea; the eye at onoe comprehends its vastness, 

 owing to what Dr. M'Culloeh has called its " sudden and unex- 

 pected magnitude," especially when l\ic summit is invested 

 with floating mist; and while speculations naturally force them- 

 selves upon the mind of the spectator, whether geologist or 

 bird-hunter, regarding the time when in awful convulsion tlie 

 great, mass first upheaved its " broad bare back into the 

 clouds," it must be confessed iis present aspect is uncommonly 

 peaceful, forming a scene, indeed, hi which are combined many 



