22 



EMBKYOLOGICAL MONOGRAPHS. 



PLATE VI. 



Development of the Discoidea and Siphonophora. Figures from Alexander Agassiz, Carl 

 Chun, J. Walter Fevvkes, Ernst H^ckel, Elias Metscunikoff, mid P. E. Mullee. 



Anterior. 



Anterior nectocalyx. 



Axis. 



Ciiainber or tube in the primitive hy- 



drophyllium, which is derived from 



a cavity early formed in the ovum. 

 Cilium. 

 Cell. 

 Epi blast. 



Infolded portion of the epiblast. 

 Emliryonie tentaele. 

 Filament of the liydrocyst. 

 Stomach. 

 liud. 



Gonophore. 

 Hypoblast. 

 Large cells (vitelline cells), hypo- 



blastic ? 

 Liver ? Cluster of " brown cells." 

 Hydrophyllium. 

 Hydroeyst. 

 Interior of bell. 

 Peduncle of a tentacular appendage 



(tentacular kuob). 

 Membrane. 

 Medusa bu<I. 



A 



A. 



Mcsoblast. 



Nectocalyx. 



Neniatocyst. 



Ovary. 



Mouth. 



Undigested food in the stomach. 



Pigment. 



Pneumatocyst. 



Posterior nectocalyx. 



Polypite. 



Radial tube. 



Somatocyst. 



Tentacle. 



Umbrella. 



Velum. 



Vitellus. 



Float. 



Partitions which separate the cham- 

 bers found in the frame-work 

 supporting the sail. 



Partitions which separate the concen- 

 tric cliambers of the lloat iu the 

 disk. 



Rim of the disk. 



Feelers on the under side of the disk. 



Sail. 



1. From a .Sketch by A. Agassiz. 



1. Sexual cluster of male and female gonophores of Physalia. mils. ym. Undeveloped medusa bud. (/o^7(. Fe- 

 male gonophore 9 , male (J . 



2-4. From A. Agassiz, Exploration of the Surface Fauna of the Gulf Stream. 



Vol. VIII., No. 2, PI. VI. figs. 1, 2, 3. 



Mem. Mils. Comp. Zool. 



Sail. 



2. Young rc/(//rt in profile, hp. Liver? 6. IJim of the disk. X. Prehensile tentacle (hydroeyst ?). 



A large feeding polyp (pcdypite) hangs down from the middle of the disk on the under side. 



3. Young of the s,Tme, from below (oral view). In the centre is .seen the mouth (or). 6. 15order of the disk. 



X. Prehensile "tentacles" ? These bodies (X), like the hydrocysts of Phgsophura, are prehensile. 



4. The same, a little older, in which the ramifications of the liver extend to the disk margin or horizontal mantle. 



pgt. Central feeding polyp or polypite. X. Prehensile tentacles (hydrocysts). 



5 -7. r.iilaria. From Sketches by Fewkes. 



5. Section through Ralaria (young Porpila or Velclla ?), found with Vclclla spiralis. The section passes verti- 



cally through sail, disk border, and retracted polypite. The sail is seen to be composed of a superficial 



