198 University of California Publications in Zoology (Vou. 9 
! ! gy 
Bancroft and Esterly (1903) reéxamined the reversal in 
direction of heart-beat in the ascidian Ciona intestinalis. Their 
work is a good illustration of the seeming inexhaustibleness as a 
subject of research of almost any biological phenomenon. 
Despite the large amount of study that has been bestowed upon 
this matter, a striking fact, hitherto unobserved, was brought to 
light: ‘‘Not only does the direction of the contractions remain 
fixed while a part of the heart is connected with only one of its 
ends, but in some way a change is effected in the heart tissue 
so that the direction of the contractions still remains fixed after 
the part has been isolated from the end which was instrumental 
in producing the fixation.”’ 
The ‘‘set’’? of a beat, as it might be called, in either one 
direction or the other, the authors speak of as physiological 
polarization. Comparison of the phenomenon with the *‘habit”’ 
acquirement by the arms of the star-fish observed by Jennings, 
and to be mentioned farther on, is instructive. 
(c) Reproduction and Development 
Kofoid (1908a) has shown that in one group of unicellular 
organisms (Ceratium) the cellulose shell of the organisms is 
normally shed and renewed from time to time; that the three 
outgrowths of horns characteristic of the genus exhibit, in some 
instances at least, alternating periods of growth and rest; and 
that self-amputation followed by regeneration of the horns 
occurs. In these unicellular organisms, therefore, phenomena of 
growth and development oceur that are quite comparable with 
such phenomena in many higher organisms. This similarity 
seems to be exhibited again in the clinging together for a time 
(how long is not known) of the individuals which arise from 
one another by division. A detailed study of the members of 
these series, both qualitatively and quantitatively, might throw 
light on the important general question of the relation among 
the individuals of a lineal generation of cells. But the author 
did not have sufficient material of this particular sort to enable 
him to attack the question. 
Dr. Torrey’s work on the hydroids and anemones has touched 
a considerable range of developmental phenomena. From studies 
