The Microscope. 239 



of sand, etc. Some of these bodies are formed in and by the 

 protoplasm and are therefore true products of it ; these we may 

 call very appropriately inclavata ; whilst others are introduced 

 from the outside and such we may call inclusions. All these 

 bodies must be carefully distinguished from the protoplasm it- 

 self. Many writers, especially those treating of eggs, have mis- 

 understood this important point, by considering the scales and 

 granules of vitellin as belonging to the plasmatic substance, in- 

 stead of regarding them as simple inclavata. 



There is sometimes great difficulty experienced in drawing a 

 clear and precise distinction between the granules or the so- 

 called microsomata of the enchylema, and the inclavata proper, 

 because the latter first appear within the enchylema as minute 

 granules, and only when they have attained to a considerable 

 size is it possible to identify them as true inclavata. Practically 

 speaking, all granules may be considered as belonging to the 

 enchylema, as long as they do not modify the arrangement of 

 of the threads of the reticulum ; and those are to be considered 

 as inclavata when they press against the threads of the reticu- 

 lum and interfere with their general arrangement. 



V. The membrane of the cell. — The protoplastic mass is 

 externally limited by a true membranous layer, which von Mohl 

 calls primordial utricle. This layer is formed by a differentiation 

 of protoplasm ; and in general is in close structural relation with 

 the protoplasm itself. This membrane, retains often for a long 

 time, the same structure as the protoplasm, being composed also 

 of a reticulum and of enchylema. It is always closed and has 

 neither pores nor markings of any kind. 



When we say that every cell has a membrane, we do not mean 

 to affirm that every cell has a solid membrane distinct from the 

 protoplasm ; all we mean is that every cell has at least a mem- 

 brane such as von Mohl calls primordial utricle, and which others 

 have called limiting layer or membranous layer, etc. Carney's 

 researches have convinced him that in spite of all criticism, the 

 primordial utricle of von Mohl is to be found in all cells. PhefiFer 

 (1877) confirms this view when he declares that it is this pri- 

 mordial utricle which regulates the relation of the internal pro- 

 toplasm with the outside world. 



The solid cellulose membrane which is often formed by a dif- 

 ferentiation of the outer layers of the primordial membrane of 



