ITS FORM AND STRUCTURE. 357 



branchial (?) leaves, set on obliquely. The ultimate 

 pairs diminish gradually, and are succeeded by a few 

 pairs of rudimentary processes on each side of a 

 slender tail. 



Viscera, a simple, clear, rather wide canal running 

 through the whole length; ordinarily parallel sided, 

 but sometimes constricted so as to form a succession 

 of spindle-shaped divisions, which pass from the head 

 to the tail in rather slow pulsations, like the dorsal 

 vessel of a caterpillar. A thick oesophageal proboscis 

 was once protruded from the mouth, of an ob-conic 

 form, with a large somewhat four-sided orifice obliquely 

 terminal. No other internal structure was visible, 

 notwithstanding the .perfect transparency of the 

 animal. 



The elegant form, the crystal clearness, and th^^ 

 sprightly, graceful movements of this little swimmer 

 in the deep sea, render it a not altogether unfit vehicle 

 for the commemoration of an honoured name in 

 marine zoology. 



The skilful pencil of Mrs. Johnston, employed in 

 the delineation of the interesting forms that stand on 

 the verge of animal life, has succeeded in presenting 

 them to us w'ith peculiar truth and beauty ; and has 

 rendered an invaluable aid to the verbal descriptions 

 of her indefatigable and eminent husband. I venture 

 respectfully to appropriate to this marine animal, 

 the surname and christian name of Mrs. Catharine 

 Johnston, as a personal tribute of gratitude for the 

 great aid which I have derived from her engravings in 

 the study of zoophytology. 



Three specimens of the Johnsto?iella have come 



