16 EMBRYOLOGICAL MONOGRAPHS. 
PLATE IV. 
Development of the Tracuymepusz. igures from Hermann For, Jonn McCrapy, Ettas 
Metscanikorr, Ernst Hacker, and B. ULsanin. 
B. blp. Blastopore. S. sp. Spermatozoan. 
E. eb. Epiblast. T. ta. Tentacle. 
eb. Epiblastic cells. ta*, _ Points of attachment (tentacles 2). 
e pl. Epiplasm. ta, Tentacular prominence. 
G. ga. Stomach. tb. Chymiferous tube. 
gi}, gm?.Buds in different conditions of U. ubr. Umbrella. 
growth. Ve we. Vacuoles. 
H. hob. Hypoblast. vel. Velum. 
hb.c. | Hypoblastie cells in centre of larva. ot. Vitellus. 
hb. ta. Hypoblast in the tentacular axes. vt. m. Vitelline membrane. 
h pl. Hypoplasm. B. Star-shaped figure with dotted rays. 
L. lab. Lips. 0. Bridge connecting inner and outer 
M. man. Manubrium, cells. 
Ne 1. Nerve. al. Epiblastic cells. 
al. Nucleus. g. Rib connecting tentacular appendages 
nt cy. Nematocyst. with the bell margin. : 
O. ocy. Otocyst. ee Conical tongue projecting from the 
or. Mouth. extremity of the tentacle with 
P. pli. Folds. base surrounded by a cluster of 
S. se. cav. Segmentation cavity. nematocysts. 
Figures 11, 12, 13, 19-27, 29, 30, were arranged by the author; the remainder were arranged by A. AGAssIz. 
1-10. Polyxenia leucostyla. From Metschnikoff, Studien iiber die Entwickelung der Medusen und Siphonophoren, 
Zeit. f. Wiss. Zoil., Vol. XXIV. Pl. Ill. figs. 1,2, 3, 4, 5, 7, 8, 9, 10. 
. Free ovum just dropped in the water. 
. Ovum with four segments. 
. Segmented egg with eight segments. 
. Segmented ovum more advanced. 
» Morula. - 
6. A ciliated larva with an external (epiblastic) layer, and a spongy mass of vitelline cells. 
7. An older larva, the body of which lias beeome very much elongated, and the extremities are about to become 
tentacles. b,c. Hypoblast of the central region of the body. Ab. ta. Hypoblast of the tentacles. The 
difference hetween the cells in the two regions is evident. 
of © Pe 
8. Larva still older, in which two tentacles are formed. 
9. Larva three days old, still ciliated, showing two long tentacles and the beginning of a new pair (fa2). A 
gastro-cavity is seen in the middle of the larva below the new tentacle. 
10. Larva four days old, with four tentacles, a well-marked stomach, and mouth. In older larve of Polywenia 
four otocysts, each alternating with the tentacles, are next formed ; and later, au inerease of the number 
of tentacles, until the adult form is reached. 
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