ZOOLOGY. 307 
female in the flesh from Cape Cod, December 7th, 1871, which was 
pronounced by Prof. Baird unquestionably B. Islandica. Since 
then I have seen numbers of females and two fine adult males in 
the Boston markets, most of them shot within state limits. 
Mr. Maynard also informs me that he took two more specimens 
of Baird’s Sparrow (Centronyx Bairdii), October 14th and 15th, 
on the Ipswich sandhills, thereby confirming the hypothesis ad- 
vanced by him in the “ Naturalist’s Guide,” namely, that they are 
regular winter visitants from the North. 
The Stilt Sandpiper (Micropalma himantopus) which I see was 
recorded in a recent number of the NATURALIST as new to our 
fauna, I consider by no means rare in its migrations. Indeed, I 
have seen as many as six or seven sent into Boston market at 
one time, from Cape Cod, and in the course of a few weeks’ shoot- 
ing in August, at Rye Beach, N. H. (just north of our state lim- 
its), secured no less than ten specimens. — WILLIAM Brewster, 
Cambridge, Mass. 
Error ry Darwin’s Ortcix or Species. In the last edition of 
the above work, p. 149, Mr. Darwin misstates Hyatt and Cope’s 
law of Acceleration and Retardation in the following language : 
“ There is another possible mode of transition, namely, through 
the acceleration and retardation of the period of reproduction. 
This view has lately been insisted on by Prof. Cope and others in 
the United States. ` It is now known that some animals are capa- 
€ of reproduction at a very early age, before they have acquired 
their perfect characters,” ete. 
Prof. Cope and others have not insisted on the above proposition, 
Which we imagine to be supported by very few facts. Their theo- 
ty of acceleration and retardation states ; that, while the period of 
reproductive maturity arrives at nearly the same age or period of 
the year in most individuals of a single sex and species, the por- 
tion of the developmental scale which they traverse in that time, 
may vary much. ‘That an addition to the series of changes trav- 
ersed by the parent, would require in another generation, a more 
rapid growth in respect to the series in question, which is accelera- 
tion. A falling short of accomplishing that completeness, would 
z t from a slower growth, hence the process is termed retarda- 
tion. Vast numbers of observed facts prove that this is the great 
law of variation towards which little progress has yet been made 
