414 



MEDUS.E OF THE WORLD. 



slightly tapering, almost cylindrical, lower part. Moreover, the Atlantic specimens have highly 



colored green or pink gonads and stomach, whereas the Mediterranean variety is usually 



colorless. We may conveniently follow Gegenbaur, 1856, and call the Mediterranean form 



mucronata, whereas the Atlantic variety may be called exigua Quoy and Gaimard = CVra.n- 



formis Lesson. In Kingston Harbor, Jamaica, during March, 1909, I found a medusa 



which I can not distinguish from the typical L. mucronata which I have often seen at Naples, 



Italy. 



Liriope mucronata Gegenbaur = a variety of L. exigua. 



Liriope mucronata, Gegenbaur, 1856, Zeit. fur wissen. Zool., Bd. 8, p. 257, taf. 8, fig. 17.— Keferstein und Ehlers, 1861, 

 Zoolog. Beitrag., p. 92, taf. 14, fign. 5, 6.— Metschnikoff, E v 1886, F.mbryol. Studien an Medusen, Wien, pp. 23 (egg), 

 36 (segmentation), 92 (development of the larval medusa), taf. 5, fign. 2-25; taf. 6, fign. 1-3. 



Eurybiopsis anisostyla, Gegenbaur, Ibid., p. 247, taf. 8, fig. 12 (larva). 



Liriantha mucronata, Haeckel, 1879, Syst. der Medusen, p. 288. 



The characters of the Mediterranean medusa are given in the synoptic table showing the 

 distinctions between the various species of Liriope. The development of Liriope mucronata 

 has been studied by Metschnikoff, 1886. The egg is 0.135 mm - in diameter and is laid between 



3 and 4 in the afternoon in December to March in 

 the Mediterranean. It is expelled from the mouth 

 of the parent medusa and is surrounded by a 

 mucilaginous envelope. The ectoplasm of the egg 

 appears granular, while the endoplasm is "vacuol- 

 ated" or foam-like. Segmentation is total and 

 equal, so that at the 16-cell stage we have a small 

 central segmentation cavity surrounded by cells, all 

 of equal size. These 16 cells then divide trans- 

 versely, thus giving rise to 16 inner cells with foam- 

 like protoplasm which are destined to form the 

 entoderm, while the 16 granular superficial cells 

 form the ectoderm. The entoderm is thus formed 

 by delamination. These entoderm cells migrate 

 slightly inward and form a single-layered, closed 

 sac, which is itself inclosed within the single- 

 layered superficial sac of the ectoderm cells. A 

 transparent jelly, the gelatinous substance of the 

 future medusa, is secreted between the superficial 

 ectoderm and the deep-lying sac of entoderm. The 

 central cavity inclosed by the entoderm cells becomes 

 the gastroccele. The ectodermal cells become 

 Fig. 266.— "Liriope ccrasiformis," after Maas, in ciliated and the larva swims actively about. 



Ergeb. Plankton Eipedition=t. exigua. ^he gelatinous substance increases in thickness 



and the ectodermal cells become distended excepting at one pole where the gelatinous sub- 

 stance does not form, and finally the inner sac of the entoderm touches the ectoderm of this 

 thin-walled pole and at the end of the fifth day we have the entoderm closely applied to the 

 ectoderm at that which is to be the oral pole. These closely applied layers consist of columnar 

 cells, while the superficial ectoderm of other parts of the spherical larva becomes a thin, flat, 

 pavement epithelium. 



The mouth breaks through at the oral pole and 4 short, solid, nematocyst-bearing ten- 

 tacles grow out from the edge of the primary stomach, their entodermal cores being formed 

 from cells of the stomach-wall. This may be considered to be an actinula stage. The velum 

 grows out as a diaphragm-like wall from the ectoderm, so that at the beginning of the sixth 

 day the characters peculiar to the medusa make their appearance. 



Later stages in the development of Liriope have been studied by Brooks in American 

 forms. The almost spherical larval medusa flattens and the originally protrusive, lower 

 stomach-wall becomes turned inward and a bell-cavity thus develops. The upper and lower 

 stomach-walls fuse at 4 interradial places, the fused areas alternating with the 4 original 

 tentacles. The 4 radial-canals and the ring-canal are simply regions where no fusion of 



