84 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Some of the shells inhabited by Hermit-crabs at Port 

 Erin are partially covered by a brown horny crust, from 

 which rises a delicate white fluff consisting of soft-bodied 

 Zooids not provided with any cups or horny cases. This 

 animal is Hydractinia echinata, and it differs from most 

 of the larger Zoophytes both in having the body of the 

 Zooid unprotected by a hard " perisarc " and also in 

 having no free-swimming medusoid buds produced in the 

 life-history. 



Various reports upon the Hydroid Zoophytes, by Miss 

 L. P. Thornely, will be found in our volumes. Mr. E. T. 

 Browne has contributed some papers on the Medusae from 

 work done at Port Erin. 



Many of the smaller jelly-fishes of our seas are there- 

 fore merely free-swimming stages in the life-history of 

 Hydroid Zoophytes, and these are frequently spoken of as 

 " Medusoids." Some of our larger Medusae, however, 

 such as the Aurelia shown in fig. IV. are not produced as 

 buds on a fixed Zoophyte colony, but have a somewhat 

 different life-history. As fig. IV. shows, the fertilised egg 

 of an Aurelia becomes an ovate free-swimming embryo 

 which settles down and grows gradually into a Hydra- 

 like Zooid with a mouth and long tentacles. Then the 

 body becomes transversely constricted and divided into 

 many pieces, which, when completely separated, lie like 

 a pile of saucers or soup-plates. As they float away from 

 the pile each such Ephyra " is seen to be a little Medusa, 

 and these detached segments of the fixed Hydroid soon 

 grow into young Aurelias. 



Some of the larger Medusae which have masses of 

 frills and filaments hanging from the under side of the 

 bell are able to sting very severely by means of 

 microscopic capsules which, when touched, discharge a 

 barbed thread carrying probably a trace of some irritating 



