34 EMBRYOLOGICAL MONOGRAPHS, 
(eaTGVAM HY exer: 
Development of EcurinorEa, continued. Figures from JoHANNES Miter, Aucust Kroun, and 
ALEXANDER AGASSIZ, 
Spatangus purpureus. 
1, 3, 5. From August Krohn, Ueber die Larve von Spatangus purpureus. Archiy f. Anat. Physiol. u, Wiss. 
Med., 1853, Pl. VII. 
2, 4, 6. From Johannes Miiller, Ueber die Larven und die Metamorphose der Echinodermen, Vierte Abhandlung 
(1850-51), Pl. VIII. Abhandl. d. K, Akad d.-Wiss. Berlin, 1852. 
7, 8. From Johannes Miiller, Ueber die Larven und die Metamorphose der Ophiuren und Seeigel (1846), Pl. ITI. 
Abhandl. d. K. Akad. d. Wiss. Berlin, 1848. 
a: From Johannes Miiller, Ueber die Gattungen der Seeigellarven, Siebente Abhandlung iiber die Metamorphose 
der Echinodermen, 1855, Pl. V. Abhandl. d. K. Akad. d. Wiss. Berlin, 1855. 
A. First pair of dorsal arms. G. Third pair of oral arms. 
B. Second pair of dorsal arms, a. Mouth. 
c. Pair of anal arms. w'. (Esophagus. 
p. Odd anal arm. 6. Stomach. 
E. Second pair of oral arms. b!. Intestine. 
F. First pair of oral arms. o. Anus. 
1. One of the older Plutei raised by artificial fecundation, with a rudimentary odd anal arm, Dp, and a single pair 
of dorsal arms, A. 
. Older Pluteus, in which the odd anal arm, D, has greatly increased in size, and the first pair of oral arms, F, 
has made its appearance. Seen obliquely. 
3. Older Pluteus, in which the dorsal arms, A, have still further developed. Dorsal view. 
4. Older than fig. 3. The growth of the Pluteus since the last stage has been principally in the elongation of 
the oral part of the larva and the lengthening of the odd anal arm. Seen from the mouth side. 
. Pluteus somewhat older than stage of fig. 4. The dorsal arms, A, are nearly twice as long as in the preceding 
stage, and the rudiments of the second pair of dorsal arms are visible. Ventral view. 
6, Older stage, in which the second pair of dorsal arms, B, is nearly as long as the first pair, A; the rudiments 
of the second pair of oral arms, E, have also appeared. Seen from the mouth side. 
. Still older Pluteus ; the first pair of dorsal arms is somewhat longer than the second ; the third pair of oral 
arms, G, has been developed, and the anal pair of arms, c, has likewise made its appearance. 
8. Older stage, in which the resorption of the Pluteus is well advanced, the anal arms have disappeared, and a 
part of the oral portion of the larva has also been resorbed by the young Spatangus ; the spines and ambu- 
lacral suckers of the young Urchin are well seen in the anal part of the Pluteus. 
9. Fully developed Pluteus, with all its arms, just before the resorption of the Pluteus begins. 
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10. Spatangoid Pluteus. From Johannes Miiller, Ueber die Gattungen der Seeigellarven, Siebente Abhandlung, 
1855, Pl. V. Quoted above. 
10. This Pluteus may he a younger stage of fig. 9, but, judging from the absence of the pair of anal arms and the 
great length of the odd anal arm, it probably does not belong to S. pwrpwreus. 
11. Echinoid Pluteus. From Johannes Miiller, Siebente Abhandlung, 1855, Pl. V. Quoted above. 
11. This remarkable Pluteus differs widely from all known Echinoid larve ; it has features in common with the 
3rachiolaria, many of its arms being flexible, without rods, These arms are perhaps only such auricles as 
we find in the Pluteus of Arbacia (see Plate IX. figs. 84, 41). It is probable, therefore, that this larva 
will prove to be the Pluteus of a Cidaris or of a Diadema. 
