206 18 



especiall}' those of Asplanchna. Narcoticising fluids maj' really help to keep the 

 animals more steady; on the other hand they die faster; then the results were onlj' 

 very badly preserved wheel organs, with the cilia without any regularity straddling 

 in all directions ; fixation and staining methods have only been used for the largest 

 males (Asplanchna and Hydatina) but even here I do not think that the result cor- 

 responded to the labour. More than a general anatomical description the methods, 

 employed by me, are not able to give; the histology of the animals cannot be stu- 

 died in this way. Owing to the exceedinglj' small size of the animals, and the 

 great difficulties connected with procuring sufficient material, this investigation 

 will be extremelj' difficult. When I have restricted the investigation strictly to the 

 anatomical description, it is because I am of opinion that the more elaborate hi- 

 stological investigations, as well as many others, do not belong to the series of re- 

 searches which should be carried out at the freshwater biological stations but in 

 a much higher degree have their natural home in the laboratories, belonging to 

 the great universities. According to my experience it is impossible for a single person 

 to carry out an investigation such as this, in all its different phases. What is gained, 

 is here as always, only a step up the ladder of our knowledge; others, with other 

 abilities and another training, may then try to take the next step. 



Chapter II. 



Systematical Remarks. 



With regard to my views concerning the systematic position of the Rotifera and 

 their mutual relationship, I will not here enter too much into details. Already in 1899 

 I tried in a paper published in Danish to reform the sj^stem of Hudson-Gosse, which 

 in my opinion is only in a very slight degree the natural expression of the mutual 

 relationship of the families. It has been a great satisfaction to meto see, that de Beau- 

 champ, (1909) whose paper inaugurates a new era in our knowledge of these 

 most interesting animals, is in accordance with mj' view upon many essential 

 points. Published in Danish, my paper has suffered the fate of being misunder- 

 stood or not understood at all, especially in the chapters relating to the wheelorgan 

 and mouthparts. As far as I have been able to see, the points of agreements be- 

 tween DE Beauchamp's and my results are more numerous than de Beauchamp 

 seems to think. The system was further adopted by Hlava (1908), and v. Hofsten 

 (1909). Now, about twenty five years later, I am quite aware that the system, even 

 if upon some points perhaps it was an advance, upon others, suffered from con- 

 sidei'able errors. De Beauchamp has tried to correct these errors; owing to insuf- 



