(;•_>«) 



THE AMERICAN NATURALIST [Vol. XLII 



strong fluid for such delicate algae, and there was evidently much 

 shrinkage of the material, as shown in the outlines of the text 

 figures. These latter are not satisfactory, considering the impor- 

 tance of the details which are discussed, and in the opinion of 

 the reviewer, are not convincing. There are some fundamental 

 principles concerned in the discussion between Oltmanns and 

 Davis which will require more thorough investigation before final 

 conclusions are likely to be readied. The most important of 

 these concern the history of the developing oogonium after the 

 multinucleate stage, and the factors that lead to the selection 



Bradley M. Davis. 



Holothurioidea. 1 — Under the above title Ostergren has made a 

 noteworthy contribution to the literature concerning the Holo- 

 thurioidea. Based upon years of special study of the group, he 

 concludes that in order to estimate the value of an organ in 

 taxonomy and phylogeny, the function of the organ must be 

 completely understood. 



Ostergren first discusses respiration, particularly in connec- 

 tion with the enteron as respiratory organ. By means of their 

 dilator muscles, sometimes the oesophagus, but most often the 

 cloaca, functions as a pump to force the water into other parts 

 of the enteron, or into especially developed extensions of the 

 same. The primitive condition is found in the Synaptidae. 



In most of the Elasipoda respiratory trees are lacking, and 

 yet the cloaca is provided with dilators, and doubtless functions 

 as a pump to force water into the enteron. As Ludwig (1889- 

 92) points out, in various members of the Elpidiidae and Psy- 

 chropotida\ a simple unpaired evagination appears as a "rudi- 

 mentary gill," or water-lung. From such a beginning comes 

 the single, or double, stemmed respiratory trees. Since it is 

 possible to have within a natural genus certain species without 

 water-lungs, others with them rudimentary, and still others with 

 well-developed respiratory trees. Ostergren maintains that the 

 presence, or absence, of these organs is of no particular impor- 

 tance in taxonomy. 



1 Ostergren, Hjalmar. Zur Phylogenie und Systematic der Seewalzen. 

 Sartryck ur Zoologiska Studier tillaguade Professor T. Tullberg. Upsala. 

 October 12, 1907. 



