M. Sar8 on the Development of Star-fishes. 239 



Fig. 3. Ovarium of a smaller individual examined 25th of February. 



Fig. 4. The same magnified, showing the very unequally developed ova. 



Fig. 5. A canal of the same ovarium still more magnified. 



Fig. 6. One of the smaller ova from this canal, showing the Purkinjean and 

 Wagnerian vesicles. 



Fig. 7. An ovum laid 7th of March. The chorion is colourless, the vitellus 

 bright red and smooth ; between the two is placed the limpid al- 

 bumen. 7' nat. size. 



Figs. 8 — 10. Exhibit the bipartition of the vitellus in the same ovum. Fig. 8, 

 on the morning of March 9th ; Fig. 9, evening of the same day ; 

 and Fig. 10, on evening of March 10th. 



Fig. 11. The young escaped from the ovum and found in the uterine cavity 

 March 17th. It is cylindrical, without visible external organs, and 

 covered by cilia. This is the first or Infusorial stage of the Star-fish. 



Figs. 12 — 20. The second or Crinoidal stage of development. 



Figs. 12, 13. Young found in the marsupial cavity March 17th, with the 

 organs of attachment sprouting forth, a a. Fig. 12 is very slightly 

 depressed or still nearly cylindrical, and exhibits the commence- 

 ment of these organs by two papillae, a a, one of which projects 

 more than the other, but by it the young can as yet not attach 

 itself. In Fig. 13 one of these papillae has divided into two, and 

 all three serve as instruments of attachment. Fig. 13 6. The same 

 young one from the front. 13' nat. size. 



Figs. 14 — 17. Young met with April 3rd in the marsupium. They are tole- 

 rably flattened, with four completely developed clavate organs of 

 attachment, a a, and a lesser papilla in the middle between them. 

 By means of these organs the young fix themselves to the walls of 

 the marsupium. Fig. 14, seen from the ventral surface, exhibits 

 the tentacula, c c, sprouting forth as very small papillae in ten rows 

 radiating from the centre of the body, two of which are approxi- 

 mated, there being two papillas in each row. Fig. 15. The same 

 young one seen from the dorsal surface. Fig. 16. Ditto from the 

 front. Fig. 17. A young specimen seen from the front, with only 

 three clavate organs of attachment. 



Figs. 1 8 — 20. Represent the transition from the hitherto bilateral condition 

 of the young to the third or radiary condition. 



Fig, 18. One of the young depicted. Figs. 14 — 16. Further developed, 

 April 15th, and seen from the ventral side. The body has become 

 pentangular, and surrounded by a border thicker and more in- 

 curved in the intervals of the five sprouting arms. The tentacles 

 become larger and more distinct, and at the end of each of the five 

 arms is perceived a small round papilla b, regarded by Ehrenberg 

 as an eye. 



Fig. 1 9. The same young represented from the dorsal side. The circular 

 sheath distinguished by a groove from the arms. Upon the skin 

 numerous spines grow. 19' nat. size. 



Fig. 20. The same young seen from the dorsal surface April 23rd. The 

 tentacles c c are lengthened into long tubes and serve now to creep 

 with. The organs of attachment a a begin to decrease. 



Fig. 21. The same on May 4th, dorsal view. Fig. 22. Ventral view. The 

 mouth is distinct, the organs of attachment have disappeared, and 

 the young, now become completely radiary, creeps about by means 

 of its tentacles. Fig. 22, nat. size. 

 At the end of the month of May the arms had become longer and nar- 

 rower, and the number of the tentacles increased to five in each of the ten 



rows. 



