26 



EMBEYOLOGICAL MONOGRAPHS, 



PLATE VII. 



Development of the Siphonophora continued. Figures from Alexander Agassiz, J. Walter 



Fewkes, and Elias Metschnikoff. 



em. ta. 



M. VIS b. 



Anterior. 



Axis. 



Cliaiiilier in the larva, wliich ulti- 

 mately becomes a canal in the 

 primitive hydrophyllium. 



Cell. 



Canal. 



Epiblast. 



Infolding or thickening of the epi- 

 blast to form the future pneuma- 

 tophore. 



Embryonic tentacles, with embryonic 



knobs. 

 Filament of the hydrocyst. 



Stomach. 



Hypoblast. 



Hydrocyst. 



Involucrnni. 



Lateral vesicle. 



Middle layer (between epiblast and 

 hypoblast), which forms the gela- 

 tinous body of tlie hydropliyllium 

 (mesoblast ?). 



Ncetocalyx. 



Undeveloped nectocalyxes. 



Nucleus. 



Nematocyst. 



Mouth. 



Posterior. 



Paiiilla(?). 



Pigment. 



pii cy. Pneumatocyst. 



pn ph. Pneumatophore. 



pr. hy ph. Primitive hydrophyllium. 



1"J- 

 py. s. 

 pyt. 

 r. lb. 

 sac. 



Polyp. 

 Polyp stem. 

 Polypite. 

 Radial tube. 

 Sacculus. 



ser. hyph. Serrated hydrophyllium. 



T. la. Tentacle. 



t. vs. Terminal vesicle. 

 V. V. Ventral. 



vl. Vitellus. 



a. Ampulla-like enlargement of the 



canal of the first formed liydro- 

 phyllium. 



/3. Canal connecting tliis ampulla with 



that of the axis. 



7. Central tube in the serrated hydro- 



phyllium. 



f. Portion of a chamber in tlic primi- 



tive larva, which remains at tlie 

 proximal end of the canal passing 

 into the primitive hydrophyllium. 



d. Enlargement of the cavity in tlie 



tentacular knob. 



X. Point of internal attachment of the 



coiled part of the tentacular knob 

 to the walls of the body which 

 envelops it, and forms the outer 

 walls of the knob. 



1-25. Development of Jgahna. 



1-11. From the ovum to the "primitive larva." 12-20. From the primitive larva to the " AUiorybia larva." 

 21, 22. From the " Athorybia larva " to the young resembling the adult. 



1, 2. Agalma Sarsii. From Metsclinikoff, op. cit., PI. VIII. figs. 1, 2. 



1. Youngest lai-va, in which the epiblast (c 6.) forms a polar cap. The vitellus (ii^.) is jicnctrated by a proto- 



plasmic network, which divides it into a spongy mass of glass-clear cells, as in Clenophora and other 

 Sijihoaophora. The external surface is ciliated. 



2. An older larva, which has become elongated and more pyriform. The deeper layer {hb.), which is called 



endoderm (liypnblast) liy Metschnikolf, may be the beginnings of tlie chamber C. P. L. The epiblast and 

 hypoblast, probably both together, form the layer c b. 



