156 



BRITISH TUNICATA. 



can only be determined, in so minute a creature, in 

 living specimens. The blood- system, however, in the 

 living Perophora, has been very carefully observed by 

 Dr. Lister and ably described by that physiologist, in 

 his excellent memoir published in the ' Philosophical 

 Transactions,' where the author has given a full 

 account of the circulation in this animal. 



The test is thin, elastic, smooth, and perfectly 

 hyaline, and is united to the mantle throughout. The 



FIG. 85. 



FIG. 86. 









FIGS. 85 AND 86. Perophora Listen. 85, right side; 86, left side. Twenty 



times natural size. 



latter is exceedingly delicate and transparent, with a 

 few muscular fibres arranged longitudinally and diago- 

 nally in a scattered manner ; they extend from the 

 upper margin, in the region of the respiratory tubes 

 011 both sides of the mantle, to about half way down. 



The branchial sac is of a sub-quadrate form, and is 

 almost co-extensive with the pallial chamber. The 

 meshes are rectilinear ; there are only three transverse 

 primary vessels, consequently only four rows of meshes 

 or stigmata, which are proportionately large. The 



