48 MEDUSA OF THE WORLD. 



An apical projection of the bell may or may not be present; and there may or may not be 

 an axial canal extending upward from the stomach into this projection. The hydroid is 

 Syncoryne or Staundia. 



We use the name Sarsia in the sense defined by Vanhoffen, 1891 (Zool. Anzeiger, p. 442). 



In 1862, 1865, A. Agassiz described, under the generic name Syndictyon, a Sarsia having 

 reticulate nematocyst-cells upon its exumbrella, and clusters of such cells upon its tentacles. 

 These are, however, only characters of immaturity and largely disappear in the full-grown 

 medusa, which is a true Sarsia in all respects. In 1879, Haeckel formed the genus Codonium 

 to include medusae resembling Sarsia but distinguished by the possession of an apex upon 

 the bell into which a blindly-ending axial canal extends from the stomach. A bell-apex 

 and axial canal are characters which are acquired during growth in varying degrees by 

 almost all species of Sarsia, and are therefore not of generic value. 



Two European and one American species of Sarsia produce medusae by asexual budding 

 from the tentacle-bulbs or from the walls of the manubrium. Chun, 1895 (Bibliotheca Zoo- 

 logica, Heft 19, fig. 2), showed that both ectoderm and entoderm of the manubrium take 

 part in the formation of these proliferating medusae; the entoderm of the manubrium forming 

 the entoderm of the daughter medusa, and the same being true of the ectoderm. Sarsia 

 prolifera Forbes, described and beautifully figured by Haeckel, 1879, under the name Codonium 

 codonophorum, produces medusa-buds upon its tentacle-bulbs. 



The majority of Sarsia medusae are probably produced asexually by hydroids of the 

 genus Syncoryne, but at least one medusa identical with Sarsia is derived from the hydroid 

 called Staundia Dujardin, 1843. Such medusae may conveniently be placed in a subgenus 

 Staundwsarsia. A medusa which appears to be closely related to Sarsia is produced by the 

 remarkable parasitic hydroid Hydrichth vs. 



The generic name Syncoryne was restricted by Allman, 1871-1872, to designate the 

 hydroid which produces the medusa Sarsia. The name Syncoryna was first proposed by 

 Ehrenberg, who applied it to hydroids now known as Clava, Coryne, etc., and in this old 

 sense it does not apply exclusively to the hydroid of Sarsia. By general consent, Allman's 

 name has been accepted in this restricted sense, Calkins, 1899, being almost alone in main- 

 taining that the generic name of the hydroid should be Coryne. 



The commonly accepted arrangement is to retain the old name Coryne to include hydroids 

 in which the reproductive elements are produced in fixed sporosacs growing upon the 

 hydranth, while Syncoryne applies to like hydroids which, however, produce free medusae. 



Weismann, 1883, found that the germ-cells of both sexes of Syncoryne sarsii originate 

 in the ectoderm of the budding medusa, and do not wander from their place of origin, but 

 become mature in the free medusa. Goette, 1904, finds, however, that in Sarsia the sperm 

 originates and remains in the peripheral ectoderm of the manubrium of the medusa, but the 

 p gg-cells, contrary to Weismann's contention, originate in the entoderm of the medusa-bud 

 while it is still attached to the hydroid, but afterwards they migrate into the ectoderm of 

 the manubrium, where they mature. 



Many of the species of Sarsia display considerable individual variability, the colors of 

 the manubrium and tentacle-bulbs ranging from green or yellow to red. An apical pro- 

 jection and an axial vessel above the stomach may or may not be developed, and the length 

 of the manubrium at maturity is subject to much variability. Moreover, the hydroids may 

 form densely or sparingly branched colonies in accordance with environmental conditions, 

 and as is well known in S. mirabihs, free medusae are produced in early spring, whereas late 

 in the season the medusae mature while still attached to the hydroids. Much contusion has 

 been introduced into the synonymy of the genus, and different stages of the same medusa 

 have occasionally received different specific names. 



Sarsia " nodosa" Busch, 1851, appears to be the young of some European Sarsia. The 

 exumbrella of very young medusae of Sarsia are usually besprinkled with nettling cells and 

 their tentacles bear prominent nematocysts, and Busch's medusa displays both of these 

 characters. (See Hartlaub, 1907, Nordisches Plankton, Nr. 12, p. 68, fig. 64.) 



