MEM. M. C. Z, IX. No. 3.—ACALEPHS, POLYPS. 49 
47-52. Renilla reniformis Cuy. From E. B. Wilson, The Early Stages of Renilla. American Journal of Science, 
ser. 3, Vol. XX. 1880. Pl. VII. 
47. Young, bilaterally symmetrical, ciliated, free-swimming polyp with the first pair of zodids (zd.). Of the 
septa (mesenteries), the dorsal pair (d.) extends back as far as the zodids, the dorso-lateral (d.-2.) pair 
reaches the posterior end of the body, the ventro-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 (z d!.) has appeared in the median line on the dorsum, in front of the two first zodids. It is 
the ‘* Hauptzooid” of the German writers. 
49. A much later stage. The first pair of lateral zodids (1.) now have well-developed tentacles. The order of 
appearance of the paired zodids, which develop into sexual zovids, is indicated by Arabic numerals. There 
are, in addition, three (usually there are 2 pairs) rudimentary zodids opposite the bases of the first pair. 
50. A much later stage than the preceding, in a state of contraction, The primary polypite (py.) has its oral 
: extremity at the edge of the disk, and not yet turmed upward. Subsequently this and all the marginal 
zooids are forced upward and made to occupy the upper surface of the disk by the union, behind (below) 
them, of the younger zodids 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 the simple zodids of fig. 50. The small ventral chamber is always turned toward 
the centre of the disk, that is, away from the oral extremity of the sexual zodid on which it is situated. 
51°. A more advanced condition than that of the previously figured zovid. The rudiment of a new zooid (z d!.) has 
appeared on the upper side. 
52. This new zodid is fully developed, and two lateral zodids (1, 1) have appeared. 
58-56. Umbellularia (sp.?). From R. v. Willemoes-Suhm, Notes on some Young Stages of Umbellularia, and 
on its Geographical Distribution. Annals and Magazine of Natural History, ser. 4, Vol. XV. 1875. 
Pl. XVIII A. 
53. Yonng stage seen from the ventral side. The terminal polypite (py.) probably comes 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 speciinen rendered transparent. Reduced to 
one half natural size. 
54, Another and older specimen seen from the dorsal side. A fourth polypite has appeared by the side of the 
original terminal polypite and has overtaken it in size, so that there are now two terminal polypites of 
equal size but different age, and two lateral polypites (1,1) behind them. In addition, a fifth (3) has 
made its appearance in the middle of the dorsum. The zovids appear first on the ventral side as seen in 
55. A ventral view of the same specimen as the preceding, the zo0ids 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 isa median line along the dorsum which is destitute of zovids. 
57-59. Aleyoniwm digitatum Lam, From A. O. Kowalevsky, Observations on the development of Cclenterata 
(cited above). Taf. 1V B. Figs. 1, 3, 4. 
57. Section of the egg, in which may be distinguished a peripheral layer of finely granular protoplasm ( p pl.) 
and a central mass containing yolk spherules (v.). 
58. Protuberances of the finely granular protoplasm of variable size appear as the first indication of segmentation. 
These are gradually constricted ofl 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 (x/.), and a 
deep layer (ev.) begins to be formed. Gradually there is formed from the outer layer a continuous envelope 
of ectodermie cells, and the whole central mass breaks up into larger nucleated cells, as seen in fig. 37, Pl. 
XII., which, with succeeding figures, continues the illustration of the development of Aleyonium. 
