MEM. M. C. Z., IX. No. 3. — ACALEPHS, POLYPS. 23 



wall or memliiano (ml).) strctdicd over two vertical plates, wbieh are parallel, and united l>y horizontal 

 floors (/3. ). The lowest of the chambers between two floors (a) is a float. 7. Chambers (seven) situated 

 between horizontal curved partitions in the body of the disk. hp. Liver ? (brown cells). 6. Disk niar"in. 

 pift. Polypite. 

 C, 7. Ualaria, from one side. pijt. Polypite. 6. Disk rim. X. Prehensile tentacles (liydrocysts ?). a. .fail. 

 Notice the characteristic vertical lines on external wall of the sail. The form of the sail, although uidike 

 that of fig. 2, is not very distant from tliat of a Vddla a little younger. 



8, 9. From Agassiz, op. cit., ]'l. II. fig. 10 ; PI. VIII. fig. 8. 



8. Medusa of Porpita. nbr. Umbrella. 



9. Medusa of Vddla, r. tb. Radial tubes with yellow cells, uhr. Urabrelha. ta. Tentacle. Rows of ncniato- 



cysts are seen on the surface of the bell. 



10-19. From Jletsilmikolf, .Studien iiber die Entwickelung der Jleilusen und Siphonoiihnren. Zrit. f. Ifhs. Zuol. 

 Bd. .\.\IV., PI. VI. figs. 5, 7, 8, 9 ; PI. VII. figs. U, 14, 10 ; I'h XI. figs. 6, 8 ; 11. .\I1. fig. 9. 



10-15. Epihalia aurantUtca, 



10. Phmula with interior filled with spongy cells, and an epiblastic cap (c S.) on the pointed pole. a. is arbi- 



traril)' taken as the anterior pole. d.. Spongy mass of cells. 



11. Older embryo, in which a nectoc.aly.x and tentacle have begun to form. The epiblast {c. h.) rises in two promi- 



nences, the smaller of which is the bud of a tentacle (ta.), and the other a neetocalyx {ncx.) Under tlie 

 epiblast is another layer, probably the hypoblast. The epiblast forms the lining of a cavity (the bell 

 cavity). Cilia (dl.) still remain over the whole body. The whole vitellus {vl.) is taken up by the spongy 

 mass of.cells. 



12. An older embryo than the last. Although this is a faithful copy of Metschnikolf's figure, it is, like his,' 



believeil to be faulty in this partic\ilar. The course of the epiblast, after it leaves the lower surface of the 

 bell, on the side turned to tlie observer, prol)ably passes by rellection into the walls of the tentacle, instead 

 of to the upper pole of the embryo. The hypoblast closely covers the infolded part of tlie epiblast in the 

 bell, and extends, also, into the tentacles. It also forms a loop (so cy.), the future somatocyst. A 

 gelatinous layer also appears between hypoblast and external ciiililast in the neetocalyx. Whole surface 

 ciliated. 



13. Oilier larva, with the primary neetocalyx of considerable size. eb. Epiblast which lines the bell cavity (/'.) 



and is also stretched over the whole ovum. A b. A layer of hypoblast in the bell. At socp. this hypoblast 

 forms a loop, the future somatocyst. Between it (Aft.) and the epiblast of the surface of the bell is a 

 gelatinous layer ( ? it mesoblast. ) /( b. Swollen hypoblastie cells, vt. Vitellus with spongy cell mass. 

 The large projection lined by cells {hV.) becomes later a polypite. Epibulia, like Ciyxtallodcs, absorbs 

 the vitellus, which is not directly changed into the ]iolypite, as in some species of Aiialma. 



14. Older larva (primitive larva), ppt. Polypite with two layers best marked near the pointed end. socy. Soma- 



tocyst. ubr. Umbrella, vl. Vitellns. 



15. Oldest larva, hi which the vitellus is wholly absorbed, and a small hydrophylliuni [hy ph.) hns formcrl in its 



place. A second neetocalyx (a. nc x.) has formed, which, from its future position, is called the anterior; 

 It is regarded as homologous with a. ncx. of figures 30, 31. The distal end of the polypite [pyl.) is open, 

 forming a mouth, so cy. Somatocyst. Althougli the intermediate larvoe between this and the adult Epi- 

 bulia are not known, ic is probable that the larger neetocalyx, with the somatocj-st, is transitory, and is 

 later lost. It can then be supposed th.at fig. 15 corresponds with a Uonophycs larva, or a definite stage 

 (fig. 29) in the cyclical development of Muggiica. 



16-17. Gleba hippoj>us. Forsk. 



16. Embryo, with first neetocalyx beginning to form. Around the whole embryo is stretched an epiblast (cb.): 



The infolded portion of the epiblast (eiiK) forms the inner bell wall. The hypoblast [hi).) is found just 

 below these two. Whole remaiu<ler of the vitellus t.aken up by a s])ongy mass of cells, which closely 

 resemble the "fiitty cells" of Ctenophora and other ccelenterate larva;. The bell cavity probably forms by 

 a dissolution of epibl.istic cells (c b'.). 



17. Larva, with a helmet-shaped bell(»ic. ), fully formed. This stage may be called the primitive larva or 



Monophycn stage, and is homologous with figs. 14 and 29. The helmet-shaped bell is probably provisional. 

 cb. Epibliist. lib. Hypoblast, r. tb. Radial tube. vt. Vitellus. 



18. Ralistenima rnhrum. From Metschnikon", o^). cit., PI. X. fig. (i. 



Larva with primitive neetocalyx (/icc.) beginning to form, showing also the young pneumatocyst (pncy.). In 

 larv;E younger than tlus we have two layers — epiblast and hy]iobIast — fornieil first ; then an elevation of 

 both, by which a cavity is left between the hypoblast and the vitelhis. The lii'st structure formeil is a bell 

 (ncx.) ; the second (pncy.), a pneumatocyst ; and the third ((/m.), probably a tentacle. The pneumatocyst 



