NOTES AND MEMORANDA. 439 



separated from the outer covering ; the cavity between the two invest- 

 ments may be single or divided into different parts, according to the 

 extent to which the protoplasm is separated from the outer coat, and 

 it is on the separated parts, and these only, that the second or inner 

 covering is developed, and it is to be regarded as nothing more than a 

 newly formed cuticle. 



Tlie stalk is not always developed, and, where it is, it may be merely 

 a continuation of the wall of the body, or it may also have proto- 

 plasmic contents ; in either case it varies greatly in character. 



The tentacles. — While Lachmann was the first to point out the suc- 

 torial nature of these appendages, it is to E. Hertwig that we owe our 

 knowledge of the fact that they are not always suckers, but that they 

 may remain of a lower grade of differentiation and be simply prehen- 

 sile filaments ; and again, the same organism may present tentacles of 

 the two types. Varying as they may in position and in arrangement, 

 it is clear that, from a morj^hological stand-point, w'e have to do with 

 a single type of structure. Looked at thus broadly, a tentacle is formed 

 of a wall, and of the contained protoplasm ; but it is something more 

 than the pseudopodia, with which Stein, Haeckel, and Gegenbaur 

 would compare it ; it is covered by the cuticle of the skeletal mem- 

 brane, and there is evidence of a differentiation of the jjrotojjlasm along 

 the axis of the tentacle, and in the higher forms there is a spiral fila- 

 ment differentiated in this part. 



As to the symmetry of the body, we find all kinds of modifications ; 

 bilateral, quadrilateral, pyramidal, radiate, or none at all. 



Protoplasmic contents. — The protoplasm is of very nearly the same 

 character in all Acinetce ; there is a delicate outer layer, which is 

 finely granular, and a more opaque medullary mass, which is often 

 pigmented ; the endosarc is more fluid than the ectosarc, and may 

 contain small shining bodies, which are spherical or navicellar in 

 form, and closely resemble the trichocysts of the ciliate Infusoria. In 

 this substance two kinds of vacuoles may be distinguished ; one, set 

 irregularly and varying in form, while the others are pulsatile, and 

 vary in number in different species ; they appear to be always found 

 near the surface of the ectosarc, and though undergoing a systole and 

 diastole do not vary in position ; with regard to these structures it is 

 of great interest to observe that in some cases the presence of an 

 excretory canal has been noted by some observers. The nu ileus 

 appears to vary in character, from a spherical or ovoid form to 

 arborescent structures of great complexity, and the study of one of 

 these latter shows that it passes through all the possible intermediate 



Beprocluction may be effected in one of three ways ; the first and 

 simplest is by fission, but this is rarely observed ; the second is by 

 gemmation, and the third by the formation of embryos within the 

 body of the parent ; but vpith regard to these moles, the author has 

 but little to say from his own observations. 



With regard to the classification proposed by M. Fraipont, we could 

 only deal with it satisfactorily by giving it in detail, and we must 

 therefore be content to make two observations, and to refer those who 



