EXPLANATION OF THE PLATES. ^ 



PLATE I. 



Fig. 1. I'lirononiu wjassizi, shows the open end of the colony, with the four processes around 



the orifice. 

 P"ig. 2. " " three nearly adult zooids, looked at on the posterior side; /. c, 



the side of the atrial orifice, and each with :i stolon and two 



younger zooids. 

 Fig. 3. " " a single zooid seen from its right side. 



Fig. 4. " " the intestinal tract, with a portion of the branchial sac, and of the 



posterior end of the endostyle. 

 Fig. 7. " '• the atrial tentacle and the atrial sphincter muscle, with its groups 



of nuclei. 



PLATE II. 



Fig. 5, I'ljnsoma uyussizi, the circle of branchial tentacles, sliowing the larger ventral one. 

 Fig. 6. " " the ganglion and hj'pophyseal glaml and adjacent structures, 



seen from the inside. 

 Fig. 8. " •• an enlarged view of one of tiic groups of nuclei of the atrial 



spjuncter muscle. 

 Oikopleiira huxlvyi, tiie body of the animal, seen from the right side. 



'• '* the intestinal tract and gonad, seen from the ventral side. 



" " the tail. 



