84 C. F. MARSHALL. 



firmer and less dense parts, the former of which takes on the 

 form of a network or reticulum. For although it is not abso- 

 tutely certain that the structures described as intracellular and 

 intranuclear networks are in all cases denser than the rest of 

 the protoplasm of the cell, they are, I believe, generally 

 assumed by histologists to be so, and also to be protoplasmic in 

 nature. 



VORTICELLA. 



The stalk of the Vorticella contains a spiral protoplasmic 

 fibre, which is eminently contractile. This fibre, when treated 

 with the gold staining, shows no trace of the presence of fibrils, 

 having simply the appearance of undifferentiated protoplasm. 



CoiL ENTER ATA. 



Hydra. — The peculiar ectoderm cells of the Hydra are 

 important to investigate, since they are generally held to repre- 

 sent the first commencement of a muscle. Here the one cell 

 is differentiated into two parts to perform two functions, the 

 one portion to act as a sensory cell, the other to act as a 

 muscle. 



Hamann 1 describes, in the epithelial muscle-cells of the 

 hydroid polypes, a network in the body of the cell, but in 

 fibrillation in the muscular process. 



My own observations on the cells of the Hydra agree with 

 those of Hamann. Gold preparations of these cells show a 

 network in the body of the cell, but no continuation of it into 

 the muscular process (fig. 1). 



Medusa. — Striated muscle has been described as occurring 

 in the disc of Aurelia by Max Schultze, Briicke, and Virchow, 

 and in Pelagia by Kolliker. 2 



In gold preparations of muscle from the disc of Aurelia I 

 find distinct transverse striation, which, under the -^ immer- 

 sion objective, is found to be due to the presence of a network 



1 ' Orgairismus der Hydroid Polypen/ p. 15. 



3 ' Strieker's Handbook of Histology,' vol. iii, p. 551. 



