120 Marvels of Pond-Life. 



mouth and the other for the vent. A system of 

 muscles enables the alimentary tube to be retracted or 

 protruded, the former process pulling the bag in_, and 

 the latter letting it out. The mouth of the bag is, so 

 to speak, tied round the creature^s neck just below the 

 tentacles, which are the only portions of it that are 

 left free. The investing sack has in nearly every case 

 the power of secreting an external sheath, more or less 

 solid, and which branches forming numerous cells, in 

 which the members of the family live in a socialistic 

 community, having, as it were, two lives, one individual, 

 and the other shared in common with the rest. 



The whole group of tubes and cells, whatever may be 

 the form in which they are aggregated, is called the 

 Polypary, or, as Dr. AUman- prefers, the Ccenoecium 

 (common house) ; the creature he names a Polypide^ 

 (polyp-like) ; and the disk which bears the tentacles 

 Lophophore (crest-bearer). There are some more hard 

 words to be learnt before the student can enjoy himself 

 scientifically among the Polyzoa, and we shall be 

 compelled to employ some of them before we have 

 done ; but will now endeavour to describe what Avas 

 presented to our view by the specimen obtained from 

 the Hampstead Pond. 



The general aspect of a branch of Plumatella repens 

 . — the creature we have to describe — is given in the 

 drawing annexed. When all was quiet, the mouths of 

 the bags belonging to each cell were slowly everted, 

 and out came a numerous bundle of tentacles, which 



* Folyzoon is preferable, as avoiding confusion with ;poIi/pite, used 

 for another class of object. 



