268 SEA-SIDE STUDIES. 



a f)aradox necessarily fixed my thoughts for some 

 time, till at length light seemed to break in obliquely 

 from some investigations pursued respecting the rela- 

 tion of the blood to Eespiration. These investigations 

 are not yet sufficiently advanced for publication, but 

 they point unequivocally to the fact, that in the animal 

 series there is a definite relation existing between the 

 develojwient of the vascular and respiratory systems, 

 the specialisation of the one following the specialisa- 

 tion of the other."' Seen by this light, the Sagitta ceases 

 to be paradoxical ; its respnation is performed by the 

 whole surface, without the need of any special organ 

 such as gill or lungs, and this absence of a respiratory 

 ap23aratus carries away with it the need of a vascular 

 apparatus. No Eespiration, no Circulation : the one 

 necessity creates the other. 



If the Sagitta is without a vascular system, it must 

 consequently be without blood. Even so. Without 

 " blood " it is, unless we extend the term " blood '' to 

 every fluid fulfilling the office of a nutrient fluid ; an 

 extension not only obliterating the whole purport of 

 exact language in science, but finally reducing us to 

 the state of the Irishman who saw in a lake " all the 

 materials for punch — barring the whisky and the sugar 

 and the lemons ; " since when we descend to the sim- 

 plest forms of organisation, we reach a nutritive fluid 

 which is water, and nothing more. Dr Thomas Wil- 

 liams, to whose researches on the blood we owe 



* Compare on this point Bergmann ti. Leuckaet : Vergleichende 

 Anatomic, p. 170. 



