174 PROGRESS OF MICROSCOPICAL SCIENCE. 



" The known chemical properties of Haemoglobin furnish a more 

 complete explanation of its peculiar distribution in tissues. . That it 

 should occur in a circulating fluid, which is the medium of respira- 

 tion, is obviously related to those properties. Its occurrence in the 

 voluntary muscles of the most active of Vertebrata, and in the most 

 active muscles of some others (as in the case of the dorsal-fin muscles 

 of Hippocampus), is equally so ; so also its occurrence in the most 

 powerfully acting part of the intestinal muscles, those of the rectum, 

 and in the only rapidly and constantly acting muscles of the Gastero- 

 pods, namely, those used in biting and rasping. 



" To connect its occurrence in the nervous chain of Aphrodite 

 aruleata with its properties is more difficult, since we have no know- 

 ledge that this Annelid is remarkable for nervous energy. The large 

 bulk of the animal in proportion to the size of the nervous system, 

 and the deficient respiration, indicated by the very slightly developed 

 vascular system and the total absence of Haemoglobin from the fluids 

 of the worm, may be a reason for the endowment of the nervous 

 centre which has to control such a large and complicated organism 

 with a special facility for appropriating what little oxygen may come 

 in its way. 



" The complete absence of Haemoglobin from Leptocephalus is an 

 example of the submission of an auxiliary, but not an essential, struc- 

 tural attribute to an all-powerful necessity — that of transparency. 

 The absence of Haemoglobin from the transparent Annelid Alciope 

 may be similarly correlated. 



" From what has been stated above as to the Haemoglobin-bearing 

 corpuscles of Glycera, Solen, and the Vertebrata, it appears that 

 when Haemoglobin is present in the blood in corpuscles, these cor- 

 puscles are of a peculiar character, and are specially related to the 

 presence of the Haemoglobin. When that is absent, other things 

 remaining the same (as with the blood of Solen ensis and the peri- 

 visceral fluid of most Annelids), the peculiar corpuscles are absent. 

 Such things as colourless corpuscles, representative of the Haemo- 

 globin-bearing corpuscles, do, however, appear to exist in the case of 

 the fish Leptocephalus. In connection with the relation of the colour- 

 less corpuscles of vertebrate blood to the red corpuscles, and of the 

 corpuscles of the vascular fluids of Invertebrata to one another and 

 to those of Vertebrates, these facts seem to be important : the colour- 

 less corpuscles in one case are only comparable to the colourless in 

 another ; the red corpuscles are something apart, which may or may 

 not be superadded.* 



" The corpuscles of the perivisceral fluid of the Gephyrean Sipun- 

 culus nudus, which is abundant in the Gulf of Naples, present some 

 facts which are interesting in relation to the occurrence of Haemo- 

 globin ; and I may therefore draw attention to them before concluding 

 this paper. The fluid which is contained in the perivisceral cavity 

 of this worm is, as is well known, of a pale madder-red colour. It 

 contains a remarkable abundance and variety of corpuscles, the most 



* [Nate. Dec. 24th, 1872.] — The two kinds of corpuscles may he definitely 

 distinguished from one another as leucocytes and pneumocytes. 



