INTRODUCTION. XXXI 



ment, by means of which, the zooid anchors itself while 

 searching for food ; they also serve occasionally as legs. 

 They are well armed with thread-cells, the deadly power of 

 which compensates for the feebleness of the frail organism 

 in other respects, and enables it to deal with creatures 

 much higher in the scale of being than itself. 



It is interesting to watch the zooid when in quest of 

 food. Anchoring itself by some of its tentacles, it casts 

 out the remainder in all directions, elongating and attenu- 

 ating them to an extraordinary degree, and keeping the 

 extremities in a state of incessant tremulous motion, as if 

 feeling for something. 



The mouth, placed as it is at the extremity of a free and 

 extensile body, and often furnished with tentacular appen- 

 dages, is in itself well adapted for the capture of prey. In 

 the later stages of its existence, when the swimming-bell 

 has collapsed and the tentacles are no longer available, the 

 gonozooid is dependent on this organ for its supplies of 

 food. 



At first sight there appears to be a total dissimi- 

 larity between the (so-called) medusa and the polypite. 

 In general aspect and in mode of life they present a 

 striking contrast. The structural affinities between them 

 are completely veiled by the modifications which adapt the 

 sexual zooid to a free and locomotive existence. The swim- 

 ming-bell is a mask, behind which the polypite is effectually 

 concealed. We cannot wonder that the escape of the 

 (so-called) medusa from the reproductive capsule of the 

 zoophyte was at first regarded as a marvel, and excited so 

 lively an interest. But the medusiform structure (which, 

 with one or two exceptions, is characteristic of the zooids 

 that are destined for independent existence) is only a 



