together ivitk the Medusa produced from them. 359 



cines Systems der Medusen " (Sicbold and Koll. Zeitschr. 1856, 

 vol. viii. pp. 202-272), in which he appends to each species of 

 Medusa, as far as is known, the nurse-form (the Hydroid po- 

 lype) from which it originates. But without taking into con- 

 sideration that, at the present time, when we are still unac- 

 quainted with the nurses of many Medusas, and, on the other 

 hand, also with the Medusae produced from many Hydroida, 

 such a classification cannot be completely carried out in practice, 

 we should by this method be led to separate all sessile Medusas 

 budded forth by Hydroid polypes from the free- swimming forms 

 produced from similar nurses, and to place them in different 

 sections, notwithstanding that in reality they are closely related. 

 Gegenbaur, indeed, has not attempted to classify the former ; 

 nay, he even passes them over entirely in silence in the syste- 

 matic revision of the Medusae given by him. And yet these ses- 

 sile Medusae can by no means be separated from the great group 

 of the free-swimming lower Medusae, of which they are only in- 

 ferior forms, which have remained stationary on a lower step of 

 the evolution common to both. As a conclusive proof of the 

 homology of the two forms, we may adduce the fact that com- 

 plete transition-forms occur between them. Thus, according to 

 Loven, the sessile female medusoid buds produced from Laomedea 

 yeniculata, Mull., and, according to Strethill Wright, those of L. 

 dichotoma, Wr., possess radiating vessels and developed motile 

 (contractile) marginal filaments, whilst the male forms in both 

 these species, according to Schultze and Wright, have no radiating 

 vessels, and fewer and shorter marginal filaments ; the Medusa- 

 buds of Syncoryna ramosa, Loven, which are likewise sessile, also 

 possess radiating vessels and marginal bulbs or rudimentary fila- 

 ments, and their bells exhibit peculiar movements of systole and 

 diastole. These three forms of medusoid buds in Hydroida 

 consequently stand, although sessile, on a higher stage of deve- 

 lopment than those of Corymorpha glacialis and the above-men- 

 tioned species of Tubularia and Podocoryna, which are destitute 

 of radiating vessels and marginal filaments, and are immoveable. 

 By the classification of the Hydroida solely according to the 

 sexual generation or the Medusce produced from them, we should 

 therefore come to separate widely the most nearly allied nurse- 

 forms in an unnatural manner, which would be the less justifiable 

 as the species in these animals is evidently not completely repre- 

 sented by the sexual generation, which is often less perfectly 

 organized, and, so to speak, embraces a far smaller portion of its 

 developmental history than the nurse-generation. We are there- 

 fore undoubtedly right if we give up the mode of proceeding to 

 which we are accustomed in the classification of the higher ani- 

 mals, namely, regarding the idea of the species as completely 



