1891-92.] A. B. Griffiths on the Blood of the Invertehmta. 117 
these two varieties lies not only in their composition, hut also in 
the physiological functions which they perform. 
The hydrolymph carries nutriment to the tissues and organs, and 
removes waste products. As a rule it has no respiratory function ; * 
for in those animals which possess blood of the nature of a hydro- 
lymph the gaseous exchanges occur directly between the tissues and 
the surrounding medium. 
The hsemolymph has not only a nutritive, but also a respiratory 
function, and it frequently contains respiratory pigments. 
In the [blood of the Vertebrata there is only one respiratory 
pigment — hsemoglobin. In the hsemolymph of the Invertebrata 
there is not only haemoglobin, but several pigments of a respiratory 
nature; for instance — haemocyanin,! haemerythrin, chlorocruorin, | 
pinnaglobin, § and probably other pigments or proteids, which may 
have a similar function. 
The Blood of Echinoderms. 
The blood of these animals is a true hydrolymph. It is a thin 
watery liquid, holding in solution mineral matter and a small quan- 
tity of proteids, and in it float numerous amceboid corpuscles. These 
corpuscles have been described by Geddes, || and many of them 
contain variously coloured globules. Among these pigments is 
MacMunn’s echinochrome,^ which has a respiratory function ; but 
the majority of these pigments are lipochromes, and consequently 
have no respiratory function. 
Foettinger** has found hsemoglobin in the blood of Ophiactis 
virens (one of the Opliiuridea), and the same respiratory pigment 
has been found by Howells ft in the blood of Thyonella gemmata 
(belonging to the Holothuridea). In the integument of many 
* In some Echinoderms, MacMunn has proved the existence of a respiratory 
pigment in the corpuscles; but, as a rule, hydrolymph has no respiratory 
function. 
t See Dr A. B. Griffiths in Conptes Renclus de VAcademie des Sciences, t. 
cxiv. p. 496. 
t Ibid., t. cxiv. (May 30, 1892), p. 1277. 
§ Ibid., t. cxiv. p. 840. 
II Archives de Zoologie Experimentale et Gtnerale, t. viii. 
Quart. Jour. Micro. Sci., 1885. 
** Zool. Anzeiger, 1883, p. 416. 
ft Studies from Biol. Lab. Johns Hopkins University, vol. iii. p. 284. 
