EXPLANATION OF PLATE X. 

 Figs. 1 to 3, Alcyonaria. 



Fig. 1. Single polyp of Alcyonium palmatum, greatly magnified. 

 st. Stomodaeum or oesophagus ; mes. mesenteries ; m.f. 

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

 s.s. supporting spicules. 



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

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

 form the protecting cortex of the colony ; Id, spicules 

 from the supporting lamella of the stomodaeum ; Ic, 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 mesoglaea of Alcyonium digitatum. 



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



Fig. 4. A tadpole larva of Aplidium elcgans (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 metamorphosis 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. caudal 

 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 rowth and budding, to new 

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

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

 ph. pharynx ; st. stomach. 



