OBSERVATIONS ON STRIPED AND UNSTRIPED MUSCLE. 81 



tiation of the cell into firmer and less dense parts, the former of 

 which takes on the form of a network or reticulum. For although 

 it is not absolutely certain that the structures described as intra- 

 cellular 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 proto- 

 plasmic 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. 



CffiLENTERATA. 



Hydra. — The peculiar ectoderm cells of the Hydra are important 

 to investigate, since they are generally held to represent 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* describes, in the epithelial muscle-cells of the hydroid 

 polypes, a network in the body of the cell, but no 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, Brucke, and Virchow, and in 

 Pelagia by Kolliker.f 



In gold preparations of muscle from the disc of Aurelia I find 

 distinct transverse striation, which, under the ■£$ immersion ob- 

 jective, is found to be due to the presence of a network similar in all 

 respects to the network described by Eetzius and Melland in striped 

 muscle (Fig. 2). 



Actinia. — Muscle taken from the base of the Actinia and treated 

 with gold was found to consist of elongated fusiform cells, non- 



* "Organtemus der Hydroid Polypen," p. 15. 



t "Strieker's Handbook of Histology," vol. iii., p. D61. 



