580 



SCIENCE. 



[N. S. Vol. XV. No. 380. 



surface of the dish in which the eggs were 

 fertilized. The larvae thus collected are 

 placed in an aquarium of fresh sea water. 

 At the same time there are also added a 

 dozen or more pipettefls of the surface 

 sand from an aquarium containing a cul- 

 ture of diatoms. (Prepared by putting a 

 liter or more of sand, dredged from the 

 ocean bottom, in an aquarium of sea water 

 and allowing to stand several days.) The 

 jar thus stocked is now covered and set 

 (before a window, where it is well, but in- 

 •directly, lighted. 



The diatoms keep the water pure and 

 ifurnish an abundant supply of the nat- 

 ural food of the larviB, and, because of the 

 Ibalanee established in the aquarium be- 

 tween animal and vegetable life, the sup- 

 ply of oxygen is kept constant and there 

 is no need for frequent changes of water. 

 The larvae are thus protected from the de- 

 structive effects of rapid changes in tem- 

 peralure produced when fresh ocean water 

 is added to that which has stood in the 

 house. 



A number of spatangoids and sand-dol- 

 lars, which had just completed their meta- 

 morphosis on September 22, have been 

 kept in a healthy and growing condition to 

 the present time (January 1) in such a 

 diatom-stocked aquarium holding one liter. 

 The water has been changed twice during 

 the three months in order to replace the 

 salts used by the diatoms and echinoderms. 



Abnormalities in Development of Hybrid, 

 Fishes: "W. J. Monkhaus. (Read by 

 title only.) 



On the Genera of the Hydracarini: Robt. 



H. WOLCOTT. 



However much we may pride ourselves 

 en the naturalness of our present classifi- 

 cation, it nevertheless must be admitted 

 that it is a purely artificial device. Thus 

 it seems legitimate to make use of every 

 modification, however artificial it may be, 



which increases its serviceability without 

 at the same time doing violence to any of 

 our accepted ideas concerning phylogenet- 

 ic relationships. In the characterization 

 of various groups, of higher or lower rank, 

 authors have made use frequently of char- 

 acters so dissimilar as to make it difficult 

 to compare the descriptions or to reduce 

 them to such form as to make them ser- 

 viceable in a general treatment of the sub- 

 ject. If, in any group, characters can be 

 found which are of family value, others 

 which are generic, and still others clearly 

 specific, while all other variations can be 

 recognized as within the limits of specific 

 variation, systematic work in the group 

 will be greatly facilitated by the recogni- 

 tion of the fact and a clear definition of 

 the value of each factor. It is evident 

 that for each collection of forms that may 

 be treated together in this manner, how- 

 ever many may be thus included, charac- 

 ters will be found which are peculiar 

 to those forms and other characters 

 jnust be found for any other similar 

 collection. It is also evident that any 

 character which would otherwise be of a 

 given value may, if greatly developed, 

 have its value so increased as to become 

 a character of the rank next above, es- 

 pecially if accompanied by other charac- 

 ters of the higher rank. If this develop- 

 ment stand alone it is better to consider it 

 in the line of aberrancy mthin the lower 

 group. It is further desirable, as soon as 

 these characters may be determined upon 

 for any group, that for the subdivisions of 

 that group diagnoses be formulated which 

 shall bring these characters sharply into 

 contrast; and in the interest of accuracy 

 it is desirable that each of these diagnoses 

 should contain in the briefest possible 

 form a statement concerning all the char- 

 acters belonging to a subdivision of that 

 rank. Furthermore, for each group a 

 type should be selected in accordance with 



