50 NATURAL HISTORY OF OUR SHORES 



in a few drops of sea- water under the microscope, or even 

 with a pocket-lens, will show the details figured on Fig. 5. 

 No. 6 is Obelia geniculata. There are other species of 

 Obelia, but all show the same structure. 



Preparations, mounted for permanency, of some of these 

 stems with the polypi expanded are beautiful and highly 

 valued objects for the microscope. Methods for the achieve- 

 ment of this will be given further on. 



Of these Hydroid zoophytes there are a great number 

 on our shores. Some, the Campanularidce (which name 

 signifies " little bells ") form close-set fringes to the leaves 

 of the Zostera, or " sea-grass," and are there seen in 

 millions. 



Still more beautiful are the Plumularidce (a " feather "). 

 In these the stem is no longer simply branched ; it is arranged 

 in pinnate fashion on a mid-rib, like an ostrich feather, or 

 perhaps rather like the frond of a fern ; and the polypi are 

 arranged at regular intervals along each pinna, while 

 between them (in most species) occur curious little bodies 

 termed Nematophores, which are polypi of peculiar structure, 

 and the functions of which are not known. 



These beautiful forms grow at the sides of rock pools, on 

 sea-weeds, and one beautiful species always selects as its 

 habitat the tips of the leaves of Zostera. 



It is very easy to overlook these when collecting, for they 

 are so delicate and transparent that it requires but little to 

 complete their concealment. A bright sunny day is the 

 best for hunting them, for then their presence is often 

 betrayed by their shadows, which are more conspicuous 

 than themselves. A fine robust, although comparatively 

 coarse, form is often cast on shore, nearly always attached 

 tq the long stems of the podded weed Halidrys siliquosa. 

 This is Aglaophenia pluma (Fig. 19). Its colour when living 

 is a golden yellow, but when cast on shore it soon bleaches 

 to white. The reproductive capsules in this one are formed 



