and Laboratory Methods. 



2417 



raised, and the hydras resumed their normal activities. The chara has been in 

 fruit for months, and the jar has furnished an abundant growth in pure culture 

 of a large desmid and a species of Difftugia. 



Aquaria which have been well stocked with various species and maintained 

 until spring, supply interesting and instructive examples of the final transform- 

 ations of larvae of insects, and especially of the nymphs of dragon-fly. The 

 artificial warmth of the room hastens the changes so that they occur earlier than 

 in the ponds. As the time for coming out of the larval skin approaches, many 

 of the animals exhibit such marked changes in appearance and action that one 

 has only to watch them closely for a few minutes to be rewarded with an exhibi- 

 tion of the entire process of ecdysis. A. H. Cole. 

 University of Cliicago. 



The Museum. 

 VIII. 



THE HALL.— Continued. 



In showing the contrasted construction and contrasted appearance of ceil- 

 ings with girders and ceilings with columns, the two views (Figs. 30 and 31) of the 

 mineral hall and the geological hall of the American Museum are instructive. 

 Naturally, the advantages of the former, as can be claimed for it by its advocates, 

 are the free space and the absence of dust-collecting surfaces. On the other 

 hand it is clumsy in appearance, meagre in detail, expensive, and not as safe as 

 column construction. The column effect in Fig. 31 is decidedly graceful, and the 



Fig. 30. — Present Mineral Hall, New York Museum, showing girders, without pillars. 



