99 



reason it must in a natural system be necessarily referred to them. Thus there only re- 

 mains the task of assigning to it its systematic place in the order of the star-fishes. 



In the division of the star-fishes it has, as is well known, been usual according 

 to Miiller & Troschel * to have regard chiefly to 2 characteristics, namely the arrangement of 

 the water-feet in 2 or 4 rows, and the presence or absence of the anal aperture. To neither 

 of these characteristics can there however in my opinion be attributed such a systematic 

 importance, as that any natural division could be established on that basis. According to 

 the first mentioned characteristic, the star-fishes generally are divided into 2 large groups 

 or sub-orders: those with 4, and those with 2 rows of water-feet. To the former group 

 there belong only a proportionally small number of forms; while the majority of known 

 star-fishes belong to the latter group, or those with only 2 rows of water-feet. Also the 

 genus Brisinga would, on account of its biserial water-feet, have to be classed in the last of 

 these groups. The unuaturalness of this binary division of the star-fishes, will however on 

 further consideration appear manifest. 



We have thus in the genus Aster las not only forms with 4, but also with more 

 rows of water-feet; and of those star-fishes provided with 2 rows of water-feet, there are 

 several which decidedly in all other respects approach extremely nearly to those with 4 

 rows. Thus the genus Pedicellaster, with 2 rows of water-feet, stands so particularly 

 near to the genus Asterias with 4 rows, that in a natural system it must even be referred to 

 the same family. The case is similar with the 2 genera C rib r ell a and Sti chaster, which 

 are undoubtedly nearly related to each other, but which have been formerly, on account of 

 the before-mentioned difi"erence in the arrangement of the water-feet, placed in quite diffe- 

 rent sub-orders. Finally we have in the interesting form Pte raster multipes, discovered 

 by my Father, an instance of considerable variation occurring in respect of the arrangement 

 of the water-feet, even within the limits of one and the same generic type. This star- 

 fish, which otherwise, as well according to its exterior habitus as according to its whole 

 organisation, is a well defined genuine Pteraster, has for each ambulacrum 4 distinct rows 

 of water-feet; while all other known species of this genus have only 2. According to the 

 former method of division, this star-fish would therefore not only be separated generically 

 from its near relatives Pt. militaris and Pt. pulvillus, but would have to be classed in a quite 

 different sub-order, where it would stand together with forms with which it only exhibits a 

 very distant affinity. It appears already, from this one instance, clearly enough, that the 

 characteristic derived from the arrangement of the water-feet, must be entirely abandoned 

 as systematic characteristic having the value formerly attributed to it. 



Neither does the other characteristic, the presence or absence of an anal aperture, 

 appear to me to be applicable as a principle of division; and that chiefly because the aper- 

 ture which has been called anal, is frequently, perhaps in most cases, not an anal aperture, 

 but only, as in the Brisinga, a more secretory pore. This seems especially to be the case 



' System der Asteriden. 



