278 PROF. ALLMAN" ON THE RECENT BESEAECnES 



■witlistanding its being enveloped in a closely applied test, is sub- 

 jected to all the protean changes of form which are so character- 

 istic of the naked sarcode animals. 



The test is quite colourless, and possesses an areolar structure 

 like that of the shell of Arcella, from which, however, it differs 

 in its much greater delicacy and in its 'flexibility and want of 

 definite form. It possesses great extensibility and elasticity, and 

 becomes dilated or contracted in accordance with the form assumed 

 by thecontaiued protoplasm. It has a single opening through which 

 the pseudopodia are protruded, and whose diameter varies with 

 the condition of the protoplasm ; but whose position is constant 

 with regard to the nucleus, which always lies opposite to it in the 

 fundus of the test. Besides this opening, the test is quite imper- 

 forate ; and Archer was deceived in supposing that pseudopodia 

 were emitted through orifices in its sides. 



The contractile vesicles which occur along with simple, fre- 

 quently very numerous, non-contractile vacuoles, lie quite in the 

 periphery of the sarcode, and when in a state of diastole carry 

 outward for a slight distance the part of the test which lies im- 

 mediately over them. 



The pseudopodia are conical and hyaline. During progression 

 the pseudopodial opening is dilated, and the body extends itself 

 more or less over the subjacent surface, forming with its shortened 

 pseudopodia a kind of flattened foot on which the whole organism 

 glides forward. It is this mode of progression, compared by the 

 autliors to that of a gasteropod, which has suggested the name 

 of CocJiliopodiiim. 



The relations of Coe/iZjopcx/M/OT tothe Mouothalamia of Hertwig 

 and Lesser cannot be overlooked, while among these the structure 

 of its test point out Arcella as its nearest ally. Perhaps, as 

 Hertwig and Lesser remai'k, a continued study will render pos- 

 sible a union of CocJiliopodiiim with Arcella ; but in the mean time 

 it is better to regard the two genera as distinct, and to abstain 

 from -plac'mg Cochliopodimn among the Monothalamia, from which 

 it is separated by its great inconstancy of body-form. 



Gocliliopodmm pellucidum has also been examined by P. E, 

 Schulze *, who confirms in all essential points the description 

 given by Hertwig and Lesser. 



A terrestrial Arcella, which bears a considerable resemblance to 



* F. E. Schulze, " Ehizcipodenshidien," Arch, fiir mikr. Anat. vol. xi. 

 p. 337, IST.'h 



