34 EMBRYOLOGICAL MONOGRAPHS. 



PLATE XI. 



Development of Echinoidea, continued. Figures from Johannes Muller, August Keohn, and 



Alexander Agassiz. 



Spatangus purpureus. 



1 3, 5. From August Krohn, Ueber die Larre von Spatangus inirpureus. Archiv f. Anat. Physiol, u. Wiss. 



Med., 185.3, PI. VII. 



2 4, 6. From Johannes Miiller, Ueber die Larven und die Metamorphose der Ecliinodermen, Vierte Abhandlung 



(1850-51), Pi. VIII. Abhandl. d. K. Akad d. Wiss. Berlin, 1852. 

 7, 8. From Johannes Miiller, Ueber die Larven und die Metamor[diose der Ophiureu nnd Seeigel (1846), PI. III. 



Abhandl. d. K. Akad. d. Wiss. Berlin, 1848. 



9. From Johannes Miiller, Ueber die Gattungen der Seeigellarven, Siebente Abhandlung iibcr die Metamorphose 



der Echinodermen, 1855, PI. V. Abhandl. d. K. Akail. d. Wiss. Berlin, 1855. 



A. First pair of dorsal arms. G. Tliird pair of oral arms. 



B. Seeond pair of dorsal arms. ft. Mouth. 



c. Pair of anal arms. «'. (Esophagus, 



r. Odd anal arm. b. Stomach. 



E. Second pair of oral arms. b'. Intestine, 



r. First pair of oral arms. o. Anus. 



1. Oue of the older Plutei raised by artificial fecundation, with a rudimentary odd anal arm, D, and a single pair 



of dorsal arms, a. 



2. Older Pluteus, in which the odd an.al arm, D, has greatly increased in size, and the first pair of oral arms, F, 



has made its appearance. Seen oblii[uely. 



3. Older Pluteus, in which tlie dorsal arms. A, have still further developed. Dorsal view. 



4. Older than fig. 3. Tlu- 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. 



5. Pluteus somewhat older than stage of fig. 4. The dorsal arms. A, are nearly twice as long as in the preceding 



sta^e, 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. 



7. 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 arm.s, c, has likewise made its appeai-ance. " 



8. Older stage, in which the resorption of the Pluteus is well advanced, the anal arms have disappeared, and a 



part of the or.al portion of the larva has also been resorbcd by the young Spatangus ; the spines and ambu- 

 lacral s\u'kers 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. 



10. Spatangoid Pluteus. From Johannes Muller, Ueber die Gattungen der Seeigellarven, Siebente Abhandlung, 



1855, PI. V. Quoted above. 



10. This Pluteus may be 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. pnrpurcu.f. 



11. Echinoid Philrns. From Johannes Miiller, Siebente Abhamlluiig, 1855, PI. V. Quoted above. 



11. This remarkable Pluteus differs widely from all known Echinoid larvpe ; it has features in common with the 



Brachiolaria, 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. 34, 41). It is probable, therefore, th.at this l.arva 

 will prove to be the Pluteus of a Cidaris or of a Diadema. 



