10 



Mespilia globulus, PI. VII Figs. 1 and 2, one being drawn from a living 

 specimen, the other from an especially carefully preserved specimen, 

 give a striking example of this. (The Asteroid and Holothurioid larvae, 

 which have no supporting skeleton, are much easier to preserve in good 

 shape). — But then, worst of all, in many cases the skeleton was found to 

 have been dissolved. The slightest trace of acidity will result in destroy- 

 ing such fine calcareous structures; although I used always the purest 

 alcohol obtainable for the preservation of these larvae, the result proved 

 fatal in only too many cases. Traces of the skeleton are still recognizable 

 in many cases and the dissolution has generally proceeded so slowly that 

 the organic matrix of the calcareous substance may still show the shape 

 of the skeleton almost undisturbed; but for the purpose of studying the 

 morphology of the skeleton and its specific characters in the difTerent 

 larval forms it is of no use. Even the preservation in Canada balsam does 

 not give safe guarantee against the dissolution of the skeleton ; in some of 

 these larvse also their skeleton has disappeared more or less completely. 

 The matter is not simply explained by stating that the alcohol or the 

 balsam must have been acid. It may happen that while some specimens 

 have had the skeleton dissolved, others preserved in the same fluid and 

 lying side by side with them in the same jar have the skeleton well preserv- 

 ed; in the same way, of larvae imbedded in Canada balsam from one and 

 the same tube and at the same time some may have the skeleton preserved, 

 while in others it is completely dissolved. — Whatever now the explana- 

 tion may be, this dissolution of the larval skeleton has in several cases 

 considerably deteriorated the value of my researches — especiaUy much 

 of the work done on Hawaii was spoilt thereby. 



Besides the morphology of the larvae attention has also been paid to 

 the question about their distribution over the ocean. Already during the 

 author's voyage to Siam in 1899—1900 opportunities were taken to collect 

 plankton samples on the passage across the Indian Ocean, and again on 

 the passage out to the East across the Indian Ocean plankton was collected 

 daily, by means of the wash-deck pump, the water from it being sifted 

 through a usual plankton net. Although somewhat deteriorated by rust 

 such plankton samples could be very well utilized and gave very valuable 

 information about the occurrence of Echinoderm larvse in the open sea 



In the years 1910—1913 plankton samples were collected for me on 

 board the Danish cruiser "Ingolf" on its cruises to the West Indies by the 

 young naturalists H.Blegvad, P. Kramp and H. Fogh. In this way 

 six series of samples were collected across the Atlantic, which have resulted 

 in important information of the distribution of Echinoderm larvse over 

 this ocean — as also in the finding of several interesting larval types In 



