Explanation of Plate X. 



Figs. 1 to 3, Alcyonaria. 



Fig. 1. Single polyp of A Icyonium palmatum, greatly magnified. 



st. Stomodaeum or oesophagus ; rues, mesenteries ; m.f. 

 mesenterial filaments or craspeda ; g.c. gastric cavity; 

 s.s. supporting spicules. 



la, a spicule from lower end of a tentacle ; 16, a supporting 

 spicule; lc, some of the superficial-lying spicules that 

 form the protecting cortex of the colony; Id, spicules 

 from the supporting lamella of the stomodaeum ; le, a 

 spicule from the deeper parts of the mesoglaea. 



Fig. 2. A branch of Alcyonium, with polyps in various stages 

 of expansion, x 2. 



Fig. 3. Spicules from mesoglsea of A ley on ium digitatum. 



Figs. 4- to 6, also A to D, Larval Ascidians. 



Fig. 4. A tadpole larva of Aplidium elegans (Giard), just freed 



from the parent. . Viewed from left side. 

 Fig. 5. Diagram of the structure of a similar larva, seen from right 



side. 

 Fig. 6. Diagram showing stages in the metamosphosis of a: tailed 



larva into the adult sessile condition. 

 Fig, 7. A colony of Aplidium elegans, when in adult stage; 



natural size ; c.c.o. common cloacal orifices. 

 Figs. A to D, Larvae where the papillae are abnormal in number or in 



arrangement. 

 Lettering the same in all figures, viz : — a. atrium ; a.o. atrial or 

 cloacal orifice ; a.p. adhesive papillae ; c.v. cerebral vesicle ; c.n. candal 

 nerve ; br. c. branchial or pharyngeal clefts ; en. endostyle ; g. gan- 

 glion ; g.s. cells homologous to the rudimentary gemmiferous tubules 

 of other species, which give rise, by growth and budding, to new 

 individuals, when the larva becomes attached, and proceeds to form a 

 colonial mass (fide Giard) ; o. mouth ; oe. cesophagus ; nt. notochord ; 

 ph. pharynx \ st. stomach. 



