The Microscope. 361 



retained their nuclei, and so by continually adding to the number 

 every time it captured another heliazoan, to have finally attained the 

 number of one hundred, or whether it is connected with the process 

 of reproduction, I cannot say. It seems to me very probable that, in 

 the fall at least, the full grown heliazoan becomes encysted, and that 

 its protoplasm then divides and subdivides, until it is converted into 

 a mass of minute bodies which, when the cyst is ruptured, make 

 their escape into the surrounding water, and then appear as naked, 

 spherical masses of granular protoplasm with a nucleus. It may be 

 that the minute bodies acquire a covering before they escape from 

 the mother cyst, and that they then act as spores, and are carried 

 about and develop similar to the spores of infusoria. 



Of course this mode of development has never been observed in 

 the heliazoa, but it seems to me to be very probable that it does 

 occur, judging from the observed young individuals and from the 

 fact that it occurs in certain infusoria. 



Cornell Univeksity, Ithaca, N. Y., 1888. 



EXPLANATION OF PLATE. 



All the figures were drawn from life, except figure 24, which is 

 a reproduction of a figure from Dr. Leidy's work on the Rhizopods. 

 Fig. 1 , which is a heliazoan, Actinosphcei'ium eichhornii, of the very 

 youngest stage, is, in nature, 14.5 ,« in diameter. The other figures 

 are drawn with the same magnification as Fig. 1, and hence they all 

 bear the same relative size in nature as is here represented, except- 

 ing Figs. 25 and 26, which are a little too small. I take it to be of 

 much more value to the reader to have the figures drawn so as to 

 preserve their relative size, and then to know the natural size of one 

 of them, than it is to have the figures of various magnifications and 

 know the magnification of each separate figure. 



I do not wish it understood that the figure taken from Leidy is 

 relatively of the same size as the other figures. 



THE MUSCULAR COATS OF THE (ESOPHAGUS OF THE 

 DOMESTICATED ANIMALS.* 



LEONAKD PEARSON. 



HISTORICAL SKETCH. 



HUMAN anatomists are agreed that in man the muscular coat of 

 the oesophagus is composed of two more or less regular and 

 distinct layers, i. e., an external longitudinal and an internal circu- 



* Abstract of a paper read before the American Society of Microscopists, Columbus 

 meeting. 



