100 THK AMERICAN MONTHLY [April, 



order SipltoMop/iora. \tinoniia is a pclajjic organism ; tluit is 

 to sjiy. it is fouiul only in the ocean surface waters, usually out at 

 sea. It is translucent, whitisli. with luuneious \o\v^ tilainents 

 trailiuij alter a central straijjlit boily. wliici) nunes forwartl with 

 •jentle impulses. The elonjjate body is buoyed up by a bubble at 

 one end so as (o maintain an oblique but nearlv vertical position. 

 It is a hvdroid colony. A main stem runs throu«ih from the bub- 

 ble, which etjuals the base of a lixed colonv. to a terminal zooid 

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

 medusa-bells which are diverted from their reproductive function 

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

 izetl ft)r the benefit of the colony as a whole. In return they are 

 relieved of the labor of capturing and tligesting food ami are sup- 

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

 Below these are located nutritive /ooids ; these have no tentacles 

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

 main stem, and their exclusive function is to di<jest food which 

 is captureil for them by the lon<^ tentacular streamers armed with 

 formidable nettle-cells which reach out over a considerable area 

 ami sweep into their destruction innumerable <leni/.ens of the 

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

 base of the tentacle and feeding persons are covered by broad 

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

 above downward. The main stem carries modified medusa; 

 which produce the generative elements and throw them ofl' into 

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

 mia 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 seiies like that 

 we have been considering. Other forms i:)f Siphonophores 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-uf-war. 



A Sli<niig-('amag(' and Stjigc for the Microscope. 



By GEO. WHITFIELD BROWN. Ik.. 



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. I)al- 

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

 substitute mav 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 



