BY DR. K. VON LENDENFELD. 207 



The relation between the adult . Medusa and the Hydroid 

 Zoophyte, on which it grows is similar to the relation between an 

 adult Proglottis of a Taenia and the non-sexual head of the 

 tape-worm. 



It is an accepted custom in every branch of Zoology to classify 

 a series of changing generations, according to that stage in which 

 mature ova and Spermatozoa are found, and it is as expedient to 

 do this here as in any other group of animals. 



However clear and self-evident this may appear, it has never- 

 theless not been done in the case of our Hydromedusre. 



Here the non-sexual stages, the colonies of nutritive Zooids, on 

 which the sexual stages bud, are described and classified, whilst the 

 adult Medusa is unknown or ignored. This practice has been 

 followed by most of the authors on Hydroid Zoophytes, although 

 both Haeckel and Claus have shown the fallacy of such a practice. 

 And so the value of papers on this subject, which are written 

 without the consideration of the adult Medusa, is very small. 

 Besides this, in most cases, not even the nutritive Zooids but only 

 their skeletons have been accurately described. 



Of course this is much easier and more convenient, than to 

 describe the soft Meduspe, which are difficult to obtain- and 

 preserve, and which have no skeleton at all — but it is not scientific. 



"What would an Entomologist say if the dried skins of the larvae 

 of Cecidomya were used to classify these flies, and they were accord- 

 ingly placed under the annelid worms, instead of placing them 

 according to the structure of the adult Insect in the group of the 

 nemocerous flies. It would appear monstrous, but it is only the 

 same thing that has been done in the case of many Hydroid 

 Zoophites. 



Besides describing the new forms I have found, the main object 

 of this paper is, to give a list of all the known Australian species, 

 with references. 



Before entering on the subject it may be worth while to recall 

 to the recollection of the reader a few of the most interesting, 

 points concerning the morphology and physiology of our animals. 



