MEM. M. C. Z., IX. No. 3. — ACALEPHS, POLYPS. 27 



3-5. Agahna cJcgans, Fewkes. From sketches liy Fewkes. 



3. Larva older than the last, with the polar cap more raised and a central chamber (C. P. X.). The layer c 6. 



was not observed to be diU'ereiitiated into two or more divisions, althougli it may have component parts 

 corresponding to the cpiblast, hypoblast, or even an intermediate gelatinous layer (mcsoblast). Nuclei (?) 

 were observed in the vitelline cells. 



4. Older larva, with the chamber (C P. i.) surrounded by two layers, eb. Epiblast. hb. Hypoblast. 



5. Side view of the last. Tlie chamber {C. P. L.) of the primitive elevation, which is the primitive hydro- 



phyllium, has become tube-like. d. Vitelline cells (?). nl. Nucleus (?). pig. Pigment patches, with 

 rough projections on the surface of the ovum. 



6, 7. ylgalma Sarsii. From Metsclmikoff, oj). cit., PI. VIII. figs. 6, 7. 



6. Larva, showing the first formation of the pneumatocyst, which first appears as an e|iiblastic structure (e I'.). 



eb. Epiblast. 7ns 6. Gelatinous thickening, forming the body of the primitive hydrophyllium, and des- 

 tined later to increase to a very large size, when the epiblastic layer lieconii'S a thin superficial layer of cells 

 stretched over it. f. Piecess above the spongy mass of vitelline cells. 



7. Primitive larva. A common larval condition of the Siphonophora, wliieh many genera of Physophorai and 



CalycophoriP pass through, distinguished on account of a provisional hydroi)hylliuni (or nectocalyx), cover- 

 ing as a helmet the vitellus, which may or may not pass directly into a polypite. The chamber C. P. L. 

 is lined with hypoblast Qi b.). The epiblast (c b. ) is stretched over the vitellus, and extends as a very thin 

 layer over the primitive hydrophyllium. The great size of the hydroiihyllinm is caused by the growth of 

 the miildle or gelatinous layer, jm cy. Pneumatocyst. f. PiCcess between the vitelline cells and the 

 hydrophyllium. 



8-10. Ayalma elcgans. From sketches by A. Agassiz. 



8. Larva a little older than the last. C P. L. Chamber of the hydrophyllium. jrr. litjpli. Piimitive hydro- 



phyllium. pn ctj. Pneumatocyst. 



9. Still older larva. C P. L. Chamber of the primitive hydrophyllium. ^jc liyph. Primitive hydrophylliiim. 



vl. Vitellus. Of the three buds shown in the figure, the larger is the imenmatocyst, and the two smaller 

 (lateral) the rudiments of the serrated hydrophyllia, which later assume great size. vt. Vitellus. 



10. Older larva, with the primitive hydrophyllium (pr. hy ph.) bent over so as to hide the cavity (C. P. L.), and 



expose in prolile the polypite and serrated hydrophyllium. By this moveuient the pneumatocyst (;jnc?/.) 

 is brought to the middle of the figure, while at its left are several buds, which later develop into hydro- 

 phyllia. 



11. Agalma Sarsii. From JletschnikofT, o;). cil., PI. VIII. fig. 11. 



Profile view of a larva, in which the margin of the provisional hydrophyllium has grown downward, covering 

 the vitellus, from which, however, it is free at the edges. The epiblast [eb.) appears at a projection, gen- 

 erally more or less pigmented, which is beginning to push out at the side of the ovum. The hypoblast 

 (h b.) is also visible at the same point, and also lines the chamber C P. L. The vitelline cells are some- 

 what reduced in number. There are two regions of crimson ]iigment [pig.]. The serrated hj'drophyllia 

 {scr. hy ph.) are conspicuous by reason, in part, of the large nenjatocysts in tlii'ir walls. 



12-17. Agahna elcgans. From sketches by A. Agassiz. 



12. Larva of about the same age, and represented in the same position as fig. 10, showing the serrated hydro- 



phyllia (-sr?-. /ty ?;/t. ) in prolile. pn, r.y. Pneumatocyst. vt. Vitellus. 



13. Larva, showing the relation uf the primitive hydrophyllium (pi: hyph.) and the pneumatocyst (;»! c)/. ) 



vt. Vitellus. 



14. Primitive larva, seen in profile with the spongy mass of cells (rt.) hugging closely the inner wall of the 



cpiblast. They here occupy a position similar to the same cells in EpibnUn (PI. VI. fig. XZhb). 

 2111 ph. Pneumatophore. pap. Small tubercles, not figured in other figures, and doubtfully called papillae. 

 ser. hyph. Serrated liydrnphyllia in profile. C. P. L. Chamber of the prinutive liydi'ophyllium now 

 reduceil to a tube. vt. Vitellus. 



15. Larva of the same age as the last, seen in a plane at right angles, laterally, and from below, indicating the 



position of the large cells in the vitellus (t)'.). or. Mouth, jm cy. Pneunnitocyst. scr. hy ph. Serrated 

 hydroiihylli.i. 



16. Older larva, in which the size of the seir.ated hydrophyllia (scr. hy ph.) lias greatly increased, and a terminal 



cluster of nematocysts has appeared at the distal extrenuty of a tube situated medially in the hydro- 

 phyllium. }mcy. Pneumatocyst.- 0. P. L. End of the cavity of the hydrophyllium. 



17. Larva older than the last, in which the primitive hydro)diyllium has disappeared, ami the polypite has 



become very much elongated. A single -serrated hydrophyllium {sr.r. hy ph.) is sketched on one .side, to 

 show its relations to the pneumatocyst (pncy.). Of the small buds below it, the lowest — that with four 

 black spots — is probably a tentacle, and the others are inunature hydrophyllia. 



