38 THE CELL 



frequently richer in water than protoplasm is, it may be dis- 

 tinguished from the latter even in the living cell, appearing as a 

 bright spot with indistinct outlines, or as a vesicle or vacuole. 

 But this is not always the case. In many objects, such as lymph 

 corpuscles, corneal cells, and the epithelial cells of gills of Sala- 

 mander larvae, no nuclei can be distinguished during life, although 

 they immediately become visible when coagulation, induced either 

 by the death of the cell, or by the addition of distilled water or 

 weak acids, occurs. 



In many kinds of cells, and in the lower organisms, the nucleus 

 may assume very various shapes. Sometimes it is in the shape of 

 a horse-shoe (many Infusoria), sometimes of a more or less twisted 



FIG. 18. (After Paul Mayer, from Korschelt, Fig. 12.) A A piece of the seventh appen- 

 dage of a young Phromma, 5 mm. in length (x 90). B A piece of the sixth appendage of a 

 half-grown Phronimella (x 90). C A group of cells from a gland in the sixth appendage of 

 a Phronimella ; the nucleus is only shown in two cells (x90). 



strand (Vorticella), and sometimes it is very much branched, 

 stretching into the protoplasm in every direction (Fig. 18 B, C). 

 This latter form chiefly appears in the large gland-cells of many 

 insects (in the Malpighian tubes, in the spinning and salivary 

 glands, etc.), and similarly in the gland-cells of the crustacean 

 Phronima. 



The size to which the nucleus attains is generally proportional 

 to the size of the mass of protoplasm surrounding it; the larger 

 this is, the larger is the nucleus. Thus, in the great ganglionio 



