1895.] Embryology. 867 
maintains, that “ the cheyletinz, parasites of birds, comprise the genus 
Cheyletus, Harporhynchus, and Picobia; and in regard to Heller’s 
genus, Syringophilus, the same writer says, p. 236, “ for these Acarina 
he (A. Heller) created the genus Syringophilus which evidently enters 
into the genus Picobia, and he has described two species in it which 
ought to be named Picobia bipectinata and P. uncinata.” The various 
immature stages and the unsettled condition of this group of Acarina, 
together with an almost total absence of American literature has made 
it an unusually difficult field for students taking up this line of work. 
However this may be, we are thankful for the timely discussion, or I 
may say criticism, raised by Mr. Trouessart on my species, and the ex- 
pression of his views upon a subject which he is conceded to be an emi- 
nent authority. If the form Picobia villosa from the black flycatcher 
is what he claims namely: The same as the European species above 
mentioned, we are pleased to have the matter straightened, also the point 
emphasized of the caution necessary in presenting as new, immature 
stages of these Acarina, sometimes so very different from the adult, 
and with shades of individual differences, even from localities as widely 
separated as Europe aiid America. —Dr. J. L. Hancock. 
Chicago. 
EMBRYOLOGY.’ 
Conjugation in an American Crayfish.—The following obser- 
vations upon the breeding habits of Cambarus affinis show how much 
difference there is between the American crayfish and the European 
form, Astacus, and serve to clear up some important structures of 
hitherto unknown use. 
Some specimens brought from Washington, D. C., in November, 
1894, immediately united in pairs when put into a shallow vessel of 
water, The same specimens and also others received in February 
paired during February, March and April. About a dozen cases were 
carefully observed with the following results: 
In captivity the entire process of conjugation lasts from two to ten 
hours and may be repeated by either animal with some other. 
1 Edited by E. A. Andrews, Baltimore, Md., to whom abstracts, reviews and 
preliminary notes may be sent. 
