100 THE AMERICAN MONTHLY [April, 



order Sifhonophora. N'anomia is a pelagic organism ; that is 

 to say, it is found only in the ocean surface waters, usually out at 

 sea. It is translucent, whitish, with numerous long filaments 

 trailing after a central straight body, which moves forward with 

 gentle impulses. The elongate body is buoyed up by a bubble at 

 one end so as to maintain an oblique but nearly vertical position. 

 It is a hydroid colony. A main stem runs through from the bub- 

 ble, which equals the base of a fixed colony, to a terminal zooid 

 at the opposite end ; just below the float are about 20 sessile 

 medusa-bells which are diverted from their reproductive function 

 and never become free, and their powers of locomotion are util- 

 ized for the benefit of the colony as a w'hole. In return they are 

 relieved of the labor of capturing and digesting food and are sup- 

 plied from the main stem. These persons are called nectocalyces. 

 Below these are located nutritive zooids ; these have no tentacles 

 but are hollow tubes with a terminal mouth open below to the 

 main stem, and their exclusive function is to digest food which 

 is captured for them by the lofig tentacular streamers armed with 

 formidable nettle-cells which reach out over a considerable area 

 and sweep into their destruction innumerable denizens of the 

 surface water of the ocean to be the food of the colony. The 

 base of the tentacle and feeding persons ai-e covered by broad 

 thin shields which are so placed as to lap over each other from 

 above downward. The main stein carries modified medusEe 

 which produce the generative elements and throw them oft" into 

 the water, where thev develop and form new colonies. Nano- 

 inia is thus comparable with an entire colony of other hydroids, 

 and yet its individuality is such that we are not so likely to notice 

 it as a colony except as we compare it through a series like that 

 we have been considering. Other forms of vSiphonophores are 

 even more highly specialized so that their colonial derivation is 

 even less easily discernible, such, for instance, as the beautiful 

 Porpita and the Portuguese man-of-war. 



A Slidiiig-Carriage and Stage for the Microscope. 



By GEO. WHITFIELD BROWN, Jr., 



NEW YORK. 



The following description and drawing of plan and section of 

 an improved sliding-carriage and stage for the microscope may 

 be of interest. If put into actual use it will, I hope, bring as 

 much comfort and satisfaction as it has brought to me. 



After considering the qualties useful in a good stage, Dr. Dal- 

 linger concludes (Carpenter, 7th ed., p. 169) that an efficient 

 substitute may be found for a mechanical stage in what he terms 

 a " super-stage," so arranged that the bearings shall be glass, and 

 friction reduced to a minimum. He says that " against its em- 

 ployment is the fact, first, that the slide is clipped into a rigid 



