195 



esting feature that the ventral median process is transformed, carrying 

 papillae, only in its lower part, while its outer part retains its normal shape 

 unaltered. This larva was taken in the Red Sea, 6/V. 1900. 



Quite a considerable number of Asteroids apparently have direct devel- 

 opment. This may fairly safely be concluded from the fact that they have 

 large, yolky eggs. It is to be expected that these forms will have only a 

 rudimentary larva as it is known in e. g. Solaster and Echinaster sepositus. 

 I have observed the eggs to be of this character e. g. in Ctenodiscus cris- 

 patus, Hippasteria phrygiana, Ceramaster japonica, Mediaster Isevis, Psil- 

 aster andromeda, Pontaster tenuispinus. In spite of many attempts I have 

 never succeeded in obtaining artificial fertilization of any of these forms. 



IV. Holothurioidea. 



The Holothurians are, next to the Crinoids, the poorest of all Echino- 

 derms for artificial fertilization. The numerous Dendrochirotes have, pro- 

 bably, all of them large, yolk-laden eggs, which completely resist artificial 

 fertilization; but also in the Aspidochirotes, where the eggs are generally 

 small and transparent, artificial fertilization is rarely successful. I have 

 myself succeeded in fertilizing and rearing the larva oi Holothuria nigra (in 

 Plymouth, 1913^)), and in the present work I have three more fertilizations 

 and rearings to record, viz. Stichopus californicus, St.Kefersteini and Holo- 

 thuria sp. But in all these cases it was only a very small percentage of the 

 eggs which were fertilized, and with many other species I tried in vain to ob- 

 tain fertilization. It is also rather troublesome to get the necessary material 

 for the study of the different stages of development, when only a small cul- 

 ture is available. A much more easy way to obtain fertilization and normal 

 development of the larvae is that employed by Selenka^) and Edwards^), 

 who put a number of specimens together in a large live-box, the cracks 

 and upper side of which were covered by gauze, the box then being sunk 

 to the bottom in an easily accessible place in the sea, in a depth of ca. 

 P/a meters. Fertilized eggs were then soon after found in considerable 

 numbers lying on the bottom of the box, and the embryos thus secured 

 were found to develop normally. For obtaining the normal larvae this 

 method will doubtless prove to be excellent in many cases, not only in 

 Holothurians but in many other kinds of marine animals which do not 



1) Th. Mortensen. On the development of some British Echinoderms. Journ. Mar. 

 Biol. Ass. X. 1913. p. 17. 



2) E. Selenlca. Zur Entwickelung der Holothurien (Holothuria tubulosa und Cucu- 

 maria doliolum). Zeitschr. f. wiss. Zool. XXVII. 1876. p. 157. 



^) Ch. L. Edwards. The development of Holothuria floridana Pourtal6s with especial 

 reference to the ambulacral appendages. Journ. of Morphology. XX. 1909. p. 212. 



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