ing new cultures from it. Several times it was tried to start new cultures 

 in the way indicated by Allen and Nelson^ and thus far successfully. 

 Still, I never succeeded in getting the same species of Nitzschia or any other 

 organism, which was so well fit for serving as food for the larvae, and the 

 full use of such food cultures was not obtained. In the last working place, 

 Tobago, B. W. I., this way of rearing the larvae was then given up, and 

 instead the larvae were given fresh sea-water every day — a considerably 

 more troublesome way of rearing the larvae, but otherwise perfectly 

 successful. 



I may point out here that, while the Nitzschia-food has proved excellent 

 for Echinoid-, Asteroid- and Holothurioid larvae, it appears to be not 

 well accepted by the Ophiuroid larvae. In the stomach of these larvae is 

 very often found the skeletons of different Silicoflagellates. If cultures 

 could be raised of these forms, they would doubtless prove to be excellent 

 for rearing the Ophiurid larvae, which would be of considerable importance. 

 Possibly other Flagellates would also prove successful. 



The main object of my work being, as stated, the comparative study 

 of the larval forms it is only a matter of course that not much attention 

 was paid to the embryological processes — cleavage, enterocoel formation 

 etc., as well as the process of metamorphosis or the postembryonal develop- 

 ment. Not that I think the study of these processes of minor importance; 

 on the contrary, I feel convinced that such studies carried out on different 

 forms will give most important correctives to the results reached from the 

 comparatively few forms hitherto studied in these regards, such as was 

 the case with the Crinoids studied by the author. But there was simply 

 no time to do all that work; having to do all the work myself: collecting, 

 preserving, making biological observations, rearing cultures etc., I had 

 simply to confine myself to studying the stages especially important for 

 my purpose; only in cases where unusual features were observed more 

 attention was paid to the embryological processes, as e. g. in Peronella 

 Lesueuri. 



As a consequence of my having altogether too much work to do I could 

 not always get the nesessary time for making drawings of the living larvae, 

 which was also in several cases impossible on account of the conditions under 

 which the cultures were reared. In such cases the different stages of the 

 larvae were carefully preserved for future study at home, partly in alcohol, 

 partly mounted in Canada balsam. Now this resulted in some very serious 

 drawbacks. It is, upon the whole, a very difficult thing to preserve such 

 larval forms as the Echinoid- and Ophiuroid larvae quite satisfactorily; 

 the arms generally shrink considerably, though not in length, of course, 

 the skeletal rods preventing a shortening. The two figures of the larva of 



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