195 



esting feature that Ihe ventral median process is transformed, carrying 

 papilla', only in its lower part, while ils outer part retains its normal shape 

 unaltered. This larva was. taken in the Hed vSea, 6/V. 19()(). 



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. Sohisler and Echinastcr sepositus. 

 I have ob.served the eggs to be of this character e. g. in Clenudiscus cris- 

 patus, Hippasteria phrygiana, Ceramasler japonica, Mediasler lievis, Psil- 

 aster andiomeda, Pontaster tenai.spinus. In spite of many attempts I have 

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



IV. Holothurioidea. 



The Holothurians are, next to the (>rinoids, 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: ])ut also in the Aspidochirotes, where the eggs are generally 

 small and transj)arent, artificial fertilization is rarely successful. I have 

 myself succeeded in fertilizing and rearing the larva of Holofhuria nigra (in 

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

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

 Iharia sp. Hut 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. 

 1 V2 nieters. 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 larvse this 

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

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



') I'll. .Mortcnscn. On llic (IcvclopiiR'nt of soinc Hritisli Ei-liinotlenns. .loiini. .Mar. 

 liiol. Ass. ,\. 1918. p. 17. 



') E. Selenka. Zur Entwickcliing der I Inlolliiitii'ii (I loldlliuria lubulosa uiul Cucu- 

 niaria doliuluin). /.i-ilsclir. f. wiss. Zool. X.WII. 1,S7(). p. I.")". 



') Cli. L. l^dwards. The di'vclopmenl of I lolotliiiria lloridana I'ourtales with especial 

 reference to the ainhulairal appoiidatj;cs. .louni. of Morphology. XX. 1!)09. i). 212. 



25* 



