98 TlIK AMKKUA.N MONTHLY | April, 



reproduce sexuallv or roumi other colonie> likf tlic oiu' from \\ liicli 

 they sprang. These nie(his;u are broad ami Hal. not hell-shaped, 

 and have no veil, hut they have niarjjjinal tentacles, radial vessels 

 maniihriuiu, and mouth. (The ilevolopment of the ohelia egg 

 is tlescrihetl hv lladilon. Practical Emhryoloi:;y, p. .[q.) 



SkK ri I.AKIA riMII.A.* 



Here, as in Ubelia, we have a colony of extremely minute 

 zooids. the colony itself having the appearance of a plant, 

 whence its name of sea-moss has been applied to it. The 

 colonies are generally found abundantly on the green rock- weeds 

 ( /v/f//.v), .so verv numerous on the rocky shores of the New 

 Hnglantl and Middle States. The colony as a whole is short 

 and usuallv closely applied to the rock- weed. It consists of a 

 central stem and lateral branches which arise from it and slant 

 awav from the base of the colony. The stem appears to be 

 notched ; these notches when closely examined reveal the 

 chitinous hvdrotheca-, which lodge the extremely small 

 feeding zooids. The cups are sessile on the stem, not stalked 

 as in Obclia. and they are opposite each other (they are 

 alternate in Hydralhnafiia) ^ and each one has a little cover, 

 operculum, to close the end of the hydrotheca when the zooid 

 is retracted. The feeding zooids arc connected by the fleshy 

 main stem, so that,as in all hydroidcolonies, thecombinetl product 

 of their digestive processes can form a sort of blood, and circu- 

 late throughout the entire colony and supply every member. 

 The colony includes, besides the feeding zooids, fewer gono- 

 zoids ; these are contained in larger capsules of chitine ; they 

 present a stem which produces medusas by budding. The medusa?, 

 in the case of 5". pumila^ however, and in many of its allies, have 

 no mouth and never become free, but they produce eggs or 

 spermatozoa, and set them free, after which they are of no 

 further use to the colony. 



NaNOMIA CARA.f 



In all the hydroids mentioned up to this point I think any one 



*BiBLioG. — Agassiz, Seaside Stud., p. 66. 



Packard, (S. abielinai Zool., p. 6i. 



S. argentea, Riv. Nat. Hist., p. 86. 



Explanation of the Fic;uke op Sbrt. pumila. 

 St. , common stem of one of the ultimate suudivisions. 



Hy, single feeding zouid, and shows also its hydrotheca ; the operculum shows in the one 

 above. 

 Gon, a gonozooid stem ; the sexual buds, and the large gonothcc.-) covering them. 

 tliiBLlOG. — Agassiz, Seaside Studies, p. 76. 



I^nkcster K. r.ritl, ix, p. 564. 



Fewkcs, Bull. Mus. Comp. Zool., xiii, p. 213. 



Huxley, Oceanic Hydrozoa. 



Explanation of Fict;RB op Nanomia taba. 

 From Fcwkes with slight changes. 

 Fl, the float at the closed end of the main stem. 



St, the main stem, at the lower end of which is the p;ircnt zooid of the colony. 

 Nc, nectocalyx or sterile bell for swimming. 

 Hy, one of the feeding zooids. 

 Ten, portion of one of the icntaclef. 

 Gon, gonozooids. 

 Sc, hydro-phyllum or scale covering the zooids. 



