356 



PLATE VII 



Fig. 1. Very thin section through the liver of Rana esculenta. Picro- 

 sulphuric-osmic acid, iron-hsematoxylin, water. Region at which three 

 cells meet. Protoplasmic structure and alveolar layer very distinct, 

 x about 3500. 



Fig. 2. Very thin section through a peritoneal cell of the gut of Branchiob- 

 della astaci Od. Picro-sulphuric acid, gentian violet, water. Thickness 

 of the section at most about equal to the diameter of a single mesh of 

 the protoplasm. The granules in the nucleus (ri) and protoplasm very 

 strongly stained. Drawn as accurately as possible. 



Fig. 3, a-c. 3, a, very thin section through the cuticle and epidermis cell of 

 Brancliiobdella astaci, showing the structure of the cuticle (c) distinctly. 

 3, b, section through cuticle of rather different nature. 3, c, surface view 

 of the cuticle. 



Fig. 4. Protoplasm of the strongly compressed living ovum of Hydatina 

 senta Ehb. The alveolar structure here exceedingly distinct. 



Fig. 5. Protoplasm of the living cells of the posterior circle of cilia of 

 Hydatina senta, from a spot where the protoplasm has not got a fibrillated 

 alveolar structure. 



Fig. 6. Small part of the protoplasm of a pigment cell of Aulastomum gulo 

 M. T. Isolated after maceration in iodine-alcohol (10 per cent). The 

 dark granules in the nodal points of the meshwork are the pigment 

 granules. 



Fig. 7. Small portion of an isolated nerve fibre of the nerve of the chela of 

 Astacus fluviatilis. Maceration in iodine - alcohol (about 10 or 15 per 

 cent), s, the sheath in optical longitudinal section with the nucleus (n) 

 lying entirely embedded in it. n', the lateral boundary of the nucleus, 

 drawn elsewhere in optical section, os, the structure of the sheath in 

 surface view. /, optical longitudinal section through the axis-cylinder. 



