10 



LUCERNARIyE AND THEIR ALLIES. 



22. It most frequently happens at the beginning of the fissigemmating period, 

 just after the scypliostoma has developed to the proper condition, that, excepting the 

 original one bearing the anterior corona of tentacles, all of the successive segments 

 across the longitudinal axis are medusoid in character, and immediately after these, 

 and while they are for from being fully prepared for an independent existence, a 

 scyphostoma-like corona of tentacles develops into an exact repetition of the 

 foremost one; but after this first crop of ephyrae has disappeared, it is a com- 

 mon occurrence to meet, in the succeeding crops, with a heterogeneous mixture 

 of ephyra>, cphyroid, doubtfully ephyroid, or doubtfully scyphostomoid, scyphosto- 

 nioid, and scyphostoma forms. Sometimes two or three scyphostoma coronse 

 succeed each other (see Agassiz, Co i Unbuttons to the Natural History of U. /S., 

 Vol. Ill, PI. xi), or two or more lie behind the ephyrte (Ag., Conirib., PI. xi. 

 Jiff. 16). Again a scyphostoma corona, following a series of ephyriT, has eye-spots 

 at the bases of the tentacles (Ag., Contrih., PI. xi, fig. 5), or the edge of a segment 

 is made up of alternate broad and narrow lobes, the first terminating in single, and 

 the latter in three scyphostomoid tentacles (Ag., Contrih.., PI. xi, fifj. 19), thus 

 imitating the ocular lobes of the ephyrae in relative position, and their composition 

 in an exaggerated form, leaving it altogether uncertain whether the segment 

 belongs to the scyphostoraic or the ephyra morph ; or again a number of ephyroid 

 segments have their ocular lobes either tipped with scyphostomic tentacles (Ag., 

 Contrih., PI. XI, figs. 15 and 22), or tlie latter are superadded close to the base of 

 the ocular peduncle (Ag., Contrih., PI. xi,figs. 8, 14, and 16). 



23. This is enough for the present to warrant us in assigning the ephyra and 

 the scyphostoma to the same morph, thereby intimating that neither the elaboration 

 of the one nor of the other necessarily has any reference to the formation of a 

 particular kind of organ, but simply indicates that this is the method by which 

 the dificrcnt varieties of the cephalic morpli are developed and repeated antero- 

 postcriorly along the longitudinal axis of tlio individuum. 



§ 5. The individual it ij of Pelagia and LucemaricB. 



24. The Pelagia which we have mentioned (20) retains its individuality in almost 

 the strictest sense of which we have any example, in fact only the less so than in 

 the highest vertebrates, because its dorso-ventrally repetitive element is less diff"er- 

 entiated and more multiplied in its results. 



25. The case of the Pelagia of Krohn brings us now directly to the consideration 

 of the nidividuality of Lucernaria?. These ccenotypic forms of Acalephte are only 

 less individualized than Pelagia, because two varieties of one morph, viz., the 

 hydroid and the medusoid, inseparably interfused, are patent to our senses in tlie 

 same unit of form ; memorizing, as it were, the separate condition of the hydroid 

 and medusoid cephalisms among the lower, most indeterminately repetitive Hydro- 

 medusiB. 



26. A Lucernarian might be compared with a scyphostoma which, instead of 

 developing the anterior segment into the most usual form, with its numerous, long, 

 slender tentacles, has evolved from itself another variety of the same morph, a 



