A MONOGRAPH OF THE EXISTING CRINOIDS 303 



special preferences regarding objects to which to attach themselves Mortensen tried 

 putting several different things into the jars with the larvae. He tried algae, especially 

 Udothea and Corallina, coral pebbles, bivalve shells, and leaves of Zostcra (Thalassia 

 testudinum). Although individuals attached themselves to almost all these objects, 

 they did not prove equally favorable. The most favorable attachments were made 

 upon Udothea and Corallina. A good many individuals attached themselves to the 

 surface film of the water and here they developed into very fine pentacrinoids. 



The greater number of the individuals that attached themselves to the Thalassia 

 leaves dropped off and fell to the bottom of the jar, but continued developing lying on 

 the side unattached. This had, however, a curious effect on them. The vestibulary 

 invagination did not close up and the thickened skin of the bottom of the invagination 

 continued to be in contact with the anterior (by this time posterior) end, by which 

 they should have been attached. This thickened skin therefore acted as a band keep- 

 big the (now) anterior end of the embryo down. As the columnals kept on growing 

 normally the stem became more and more curved, the result being that the embryo 

 assumed a peculiar shape resembling a pipe. Even in spite of this abnormal shape some 

 of these specimens went on growing and at last developed into pentacrinoids differing 

 from the normal ones only through having the head bent downward, and Mortensen 

 said that he can scarcely doubt that it would have been possible to rear them to full 

 development if time had permitted. 



On account of the brevity of his stay at Tobago Mortensen did not succeed in 

 getting the pentacrinoids very far in their development. On leaving the island he 

 carried some of his cultures with him in the hope that they might stand transportation 

 and continue their development. While staying in Port of Spain, Trim'dad, waiting 

 for the steamer for New York, he had the cultures placed in one of the laboratory 

 buildings of the Botanical Gardens through the kind permission of the director, Dr. 

 James B. Rorer. During these five days everything went well, though there was no 

 opportunity for changing the water. On board the steamer it was difficult to find a 

 suitable place for the cultures, and one night, when near New York, the temperature 

 went down too low, so that the pentacrinoids were chilled. On his arrival at New 

 York he had them placed in the Aquarium under excellent conditions, suitable tem- 

 perature, and light. Although some of the pentacrinoids were still alive, they did not 

 recover from the chilling and did not develop any further, so that he thought it useless 

 to try to carry them alive to Copenhagen and preserved them. 



Mortensen says that a difficulty in describing the development of a crinoid arises 

 from the orientation, on account of the fact that the larva attaches itself by the 

 anterior end, the posterior end of the larva becoming thus the oral end of the pcnta- 

 crinoid. He remarked that Seeliger orients the pentacrinoid in the same way as the 

 larva, head downward. Although there is a morphological reason for this, it seemed to 

 him too unnatural. Consequently he adopted the method of Bury and represented 

 both the larva and the pentacrinoid in their natural position. 



The eggs are rather small, about 0.2 mm. in diameter, opaque, whitish with a 

 faint reddish tint. On being discharged they are surrounded by a distinct clear follicu- 

 lar membrane. The peculiar structure of the follicular membrane described by 

 Ludwig in Antedon mediterranea he did not observe in Tropiometra. It is true that 

 he did not look especially for it in the living object, not remembering anything about 



