RELATION OF RESPIRATION TO CIRCULATION. 253 



ovary, if the statement of so accomplished a zootomist needs 

 confirmation. 



But the point of all others wliich in this interesting Sagitta 

 excited my interest was one I have not seen noticed by 

 others, namely, the entire absence of any vascular system. 

 Here is an animal with a nervous system of some importance 

 (see Prof Huxley's diagram in the Microscopical Journal) 

 ■with eyes, if no other organs of sense, and with muscular 

 fibres of the striped kind, yet in spite of such characteristics 

 of high organisation, it is totally without " blood," without a 

 trace of a vascular apparatus. So striking a paradox neces- 

 sarily fixed my thoughts for some time, tiU at length light 

 seemed to break in obliquely from some iiivestigations pur- 

 sued respecting the relation of the blood to Eespiration. 

 These investigations are not yet sufiiciently advanced for 

 publication, Init they point unequivocally to the fact, that in 

 the animal series there is a definite relation existing between 

 the development of the vascidar and respiratory systems, the 

 specialisation of the one following the specialisation of the 

 other.* Seen by this light, the Sagitta ceases to be para- 

 doxical ; its respiration is performed by the whole sur- 

 face, without the need of any special organ such as gill 

 or lungs, and this absence of a respiratory apparatus carries 

 away with it the need of a vascular apparatus. No Re- 

 spiration, no Circulation : the one necessity creates the 

 other. 



If the Sagitta is without a vascular system, it must con- 



* Compare on this point Bergmann 0. Leuckakt: Vergleichende 

 Anatomie, p. 170. 



