»889.] Embryology. 501 
was successful in artificial impregnation and in tracing the his- 
tories of the various segmentation planes. The first plane is 
longitudinal, and for many stages an alternation of rest and 
activity on the opposite sides of this plane is noticeable. Thus 
at one time almost every nucleus on the left side shows dis- 
tinct mitosis figures, while not a single nucleus of the right 
side exhibits such a feature. This was witnessed again and 
again, until the blastoderm contained 116 cells. 
Crustacea.— Professors W. K. Brooks and F. H. Herrick 
describe {J. H. U. Circ.,^o. 70) some features in the develop- 
ment of the Peneid form Sergestes hispidus. It escapes from 
the &g^ as a protozoea, passes soon to the true zoea stage, and 
then to a mastigopus condition. 
General.— Dr. H. V. Wilson gives an account {J. H. U. 
Circ, No. 70) of the times of breeding of several marine forms 
at the Bahamas, which will prove of value to students visiting 
the West Indies. 
Worms. — Dr. Hurst records {Notes from Leydeji Museum, 
January, 1889) the presence of Arenicola cristata (originally 
described by Stimpson from South Carolina) at Naples. 
EMBRYOLOGY. 
The Origin and Meaning of Sex.'— My hypothesis re- 
specting the origin and meaning of sex may be stated provi- 
sionally as follows, pending a fuller sketch to be published in 
the immediate future. 
I. Over-nutrition is regarded as the prime cause of the un- 
- Seventeen paraeraphs. or those numbered i, 2, 8, 9, 12 to 18, 21, 22, and 25 
f the hypothesis' here somewhat more fully prese'nte 
- Philadelphia, acfvised tl 
