MEM. M. C. Z., IX. No. 3. — ACALEPHS, POLYPS. 49 



47-52. Rcnilla rcniformis Cuv. From E. B. 'Wilson, The Early Stages of Reuilla. American Journal of Science, 



ser. 3, Vol. XX. ISSO. PI. VII. 



47. Young, bilaterally symmetrical, ciliated, free-swiiuming polyp with the first X'air of zooids (z cl. ). Of the 



septa (mesenteries), the dorsal pair (d.) extends back as far as the zouids, the dorso-Iateral (d.4.) pail- 

 reaches the posterior end of the body, the veutro-lateral is somewhat longer than the dorsal, and the ven- 

 tral pair is the shortest of all. 



48. Later stage with 8 pinnate tentacles, probably about 2 weeks after the abandonment of the free mode of life. 



A third zooid (; d<.) has appeared in the median line on the dorsum, in front of the two first zooids. It is 

 the " Hauptzooid" of the Gennan writers. . 



49. A much later stage. The first pair of lateral zooids (1.) now have well-developed tentacles. The order of 



appearance of the paired zoiiids, whicli develop into sexual zouids, is indicated by Arabic numerals. There 

 are, in addition, three (usually there are 2 pairs) rudimentary zooids opposite the bases of the first pair. 



50. A much later stage than the pi'eceding, in a state of contraction. Tlie primary polypite {l»j.) has its oral 



extremity at the edge of the disk, and not yet turned upw;«-d. Suhseipiently this and all the marginal 

 zooids are forced upward and made to occupy the upper surface of tlie disk by the union, behind (below) 

 them, of the younger zooids which bud out from the angles between them and increase in size. The rudi- 

 mentary zooids bud in a similar manner, each group becoming a kind of miniature of the whole colony. 



51. An enlarged view of one of tlie simple zociids of fig. 50. The small ventral chamber is always turned toward 



the centre of the disk, that is, aicay from the oral extremity of the sexual zoijid on which it is situated. 

 61°. A more advanced condition than that of the previously figured zociid. TIic rudiment of a new zooid (z d'. ) has 

 appeared on the upper side. 



52. This new zooid is fully developed, and two lateral zooids (1, 1) have appeared. 



53-56. Umbdhdaria (sp. ?). From li. v. Willeinoes-Suhm, Notes on some Young Stages of Umbcllularia, and 

 on its Geographical Distribution. Annals and Jlagazine of Natural History, ser. 4, Vol. XV. 1875. 

 PL XVIII A. 



63. Y^oiing stage seen from the ventral side. The terminal polypite (py. ) probably conies out first, as it exceeds 

 the others in length. In this and succeeding figures the order of the appearance of the polypites is indi- 

 cated by Arabic numerals. The rachis is shown as seen in a specimen rendered transparent, lleduced to 

 one half natural size. 



54. Another and older specimen seen from the dorsal side. A fourth polypite has ajipeared by the side of the 



original terminal polypite and lias overtaken it in size, so tliat there are now two terminal polypites of 

 eijual size but different age, and two lateral polypites (1, 1) behind tliein. In addition, a fifth (:i) has 

 made its appearance in the middle of the doi'sum. The zouids appear first on the ventral side as seen in 



55. A ventral view of the same specimen as the preceding, the zooids being indicated by dots. 



56. Dorsal aspect of a larger specimen in which the primary polypite (py. ) is supplemented by another terminal 



one. The author does not distinguish between them, but the figures seem to warrant the interpretation 

 given by the lettering here adopted. There is a median line along the dorsum which is destitute of zooids. 



57-59. Alcyonium diijitatum Lam. From A. 0. Kowalevsky, Observations on the development of Cadenterata 



(cited above). Taf. IV B. Figs. 1, 3, 4. 



57. Section of the egg, in which maybe distinguished a peripheral layer of finely granular protoplasm {i>2'^-) 



and a central mass containing yolk spherules {vl.). 

 68. Protuberances of the finely granular protoplasm of variable size ap|iear as the first indication of segmentation. 



These are gradually constricted oil' from the central mass which they then envelop as an irregular layer. 

 59. This peripheral layer of cells undergoes further division. Some of the cells contain two nuclei {n/.), and a 



deep layer (f)t.) begins to be formed. Gradually there is formed from the outer layer a continuous envelope 



of ectodermic cells, and the whole central mass breaks up into larger nucleated cells, as seen in fig. 37, PI. 



XII. , which, wdth succeeding figures, continues the illustration of the development of Alcyonium. 



