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STYLASTERIDAE 



The most decisive and constant characters however are found in the condition of the gastero- 

 styles and ampullae. Whilst the gasterostyle in the preceding species was conical and twice as high 

 as broad, in Stylaster roseits it is almost transformed to a spherical lattice-work (PI. Ill, fig. 22), which 

 rests with a broad base on the bottom of the gasteropore. In fertile colonies the female gonophores 

 especially project like hemispheres above the surface of the colony; whilst the female gonophores in 

 the preceding species were equipped with spines, in the present species they are quite smooth. These 

 are important differences, which compel us to consider the colonies as representing quite different species. 



Examinition of the structure of the tissues in Stylaster rosciis reveals such small and unessential 

 differences from Stylaster gemmascens, that we can only ascribe them to the bad preservation of the 

 specimens of the present species. It is only represented in the material by dried fragments and 

 colonies, which have been placed directly in 70% alcohol. The only difference which might possibly prove 

 to have some importance is, that the large stinging cells, which are extremely seldom in Stylaster 

 gemmascens and Stylaster [Allopora) norvegicus, are fairly numerous in the stolons of Stylaster roseus\ 

 they are not found here either in the zooids. 



Most of the colonies are fertile. There is nothing to indicate that they are hermaphrodite and 

 the largest specimens, which come from the waters off Angmagsalik (Greenland), are male. The condi- 

 tion of preservation of the material did not permit any exhaustive examination of the gonophores. 

 I shall therefore only refer here to some few features, which have some interest when compared 

 with the few and scattered observations hitherto reported regarding the gonophores of the Stylasteridae. — . 

 On young developmental stages of the male gonophores (PI. IV fig. 36) we see, that the gonophore 

 has a well-developed central spadix, which however does not reach the apex of the gonophore 

 No trace could be found of an endodermal cell layer under the ectoderm, which according to Hickson 

 (1891 p. 392) surrounds the sperinarium of the gonophore in the Stylasteridae. Nor did I succeed in 

 finding indications of such a cell layer in the later developmental stages. — When the sexual cells ap- 

 proach maturity we still find a distinct spadix (PI. IV fig. 39) which extends into the spermarium to- 

 wards the centre of the gonophore. During the transformation of the spermatocytes to spermatozoa 

 the spadix atrophies and disappears in gonophores with fully developed spermatozoa. 



During the last transformation we should expect to find the development of the seminal duct, 

 which according to Hickson is characteristic of the Stylasteridae. Fig. 43 of PI. V shows the condition 

 in Stylaster roseus at a spot where the seminal duct should be expected; the picture is of a gono- 

 phore with the spermatozoa almost fully formed. A slight thickening of the ectodermal epithelium 

 can be detected both in the gonophore and on the adjacent part of the roof of the ampulla; but a 

 comparison with other gonophores indicates that this is merely a chance. Even at this place, where 

 the spermatozoa would very soon escape, we find no trace of the formation of a seminal duct. 

 The apex of the gonophore points towards a neighbouring stolon canal and at other places also the 

 conditions suggest, that the gonophores of the ampulla empty their ripe sex cells into adjoining stolon 

 canals and not directly out through the roof of the ampulla. The conditions seen cannot be explained 

 by the state of preservation, for they are the same in all the cases, where the course of the cell layers 

 can be determined with certaintv. 



