THE STRUCTURE OF PROTOPLASM. n 



mines the primary alveolar structure as described by Butschli. 

 The smaller drops ("granules ") lying between these gives rise 

 to the "secondary," or fi .er alveolar structure as described by 

 Reinke, and subsequently by Mrs. Andrews, as I understand 

 these authors. 



Relations of the Astral Rays to the MesJnvoi'k. — We may 

 now make a brief digression to consider the third question pro- 

 pounded on page 5, namely : What is the relation of the astral 

 rays and spindle-fibres to the alveolar substance .? It is easy to 

 see, both in sections and in living material, that in a well-devel- 

 oped aster the alveoli are arranged in radiating lines between 

 the astral rays (Fig. 4), precisely as Butschli and so many others 

 have described. The rays themselves are, however, something 

 more than the radially arranged inter-alveolar septa, for, in the 

 first place, they are often much thicker than these septa, and, 

 in the second place, they stain more intensely than the continu- 

 ous substance. A careful study of the rays in the echinoderms, 

 and in many other forms (especially in Nereis, Thalassemia, 

 Lamellidoris, and Ascaris), leaves, I think, no room for doubt 

 that, in sections at least, the rays are actual branching fibrillae, 

 as described by so many observers since the time of Van 

 Beneden, that thread their way through the continuous sub- 

 stance between the alveoli, often in a zigzag course. The 

 strongest evidence that they are fibrillae is given by the appear- 

 ance of the cut ends of the rays as they appear in somewhat 

 excentric or rather thick sections of the asters. In such sec- 

 tions, particularly in the case of large and coarse asters like 

 those of Nereis (Fig. 3, b), the rays may be seen in the clearest 

 manner to terminate as they pass upwards towards the eye in 

 well-defined cut ends, and I think no one who studies these 

 preparations can doubt that in them the asters are true fibrillar 

 structures. 



^ye may now inquire in what manner the rays arise and grow, 

 and what is the origin of their substance. In the growing aster 

 the rays progressively extend themselves from the centre out- 

 wards, gradually losing themselves in the general meshwork. 

 It has been maintained by some writers that the rays grow out- 

 wards from their bases like the roots of a plant, and in a certain 



