820 The American Naturalist. [September, 
In the gastrula stage when the equatorial band of cilia is formed and 
the cleavage cavity nearly closed up by the elongated entoderm cells, 
spin processes were seen at the end opposite to the area of invagination, 
passing from the ectoderm cells to the membrane where it was slightly 
raised away from the ectoderm. Here also some movement and change 
of form was seen in a process, though not satisfactorily. Within the 
cleavage cavity a moving, pseudopodium-like process appeared to 
extend out from the entoderm toward the ectoderm, but it could not be 
seen clearly. 
Some of these processes in Serpula, less difficult to see than the finest, 
presented enlargements, suggesting the probability of slow flowing of 
material along the process. The increase in number and length of 
filaments from a definite area under observation for a few minutes 
showed that they were gradually formed, and from the egg outwards. 
Owing to poor light no higher than 8 eye-piece could be used with 
2 mm. objective, so that it is probable many phenomena escaped ob- 
‘servation. i 
The occurrence of such filose activity of the surface of the eggs of an 
animal so widely separated from the echinoderms supports the idea that 
such phenomena are universally properties of protoplasm, —an hypoth- 
esis put forth in a recent work’ and based not only upon egg, and other, 
external spinnings, but upon numerous internal protoplasmic phenom- 
ena of the same nature, such as spinnings into alveoli of Bütschli’s 
structure in both fluid areas and contractile structures, and contraction 
and strial displacements of the substance. 
- E. A. ANDREWS. 
PSYCHOLOGY.! 
Some Experiments on the Tactual Threshold for the 
Perception of Two Points.’™—The term “ space-threshold ” was 
applied by Fechner to the distance which two small points must be 
apart in order to be perceived as two. Weber had already devoted 
3The Living Substance as Such and as Organism. G. F. Andrews. Gnin 
& Co. Boston. August, 1897. 
1 Edited by Howard C. Warren, Princeton University, Princeton, N. J; 
2 The first group of experiments described here were reported in the Philo- 
sophische Studien, 1897, XIII, 163-222, reprinted in Princeton Contributions te 
Psychology, II, 1-60. The second group, viz., those with successive stimuli, will 
appear in an early number of the Psychological Review. 
