90 GEORGE LEFEVRE AND WINTERTON C. CURTIS 
lected in the middle and northern sections of the United States, 
and in the absence of adequate records from higher and lower lati- 
tudes, it is impossible to sa}'- to what extent a colder or a warmer 
climate might affect the period of gravidity. That it would have 
some influence can hardly be doubted, although a distinction 
between a long and a short season will probably be found to hold 
true in general . 
The same difference has been repeatedly stated to occur among 
European Unionidse. According to Harms ('09, p. 332), for 
example, in Unio the breeding season begins early in March, or, if 
the weather is cold, not until the end of May. In Anodonta, 
which carries the larvae over the winter, the eggs are fertilized 
about the middle of August, all of the individuals entering upon 
the breeding season at nearly the same time, while by the middle 
of October almost all the females are gravid with glochidia. Mar- 
garitana breeds in July and August, according to Harm's observa- 
tions, and during that time produces tWo successive broods, from 
sixteen days to four weeks, according to the temperature, being 
required for the development of each. Although we have not 
determined it beyond all doubt, our records strongly indicate that 
the species of Quadrula, and possibl}^ some other summer breeders, 
also spawn twice during the same seasons, first in June or July 
and again in July or August. 
CONGLUTINATION OF THE EMBRYOS 
After extrusion of the eggs from the genital aperture, they are 
passed along by ciliary action to the cloaca, and thence by suction 
according to Latter ('91, p. 53), are drawn back into the supra- 
branchial chambers. Here they are fertilized by spermatozoa 
brought in with the incoming current of water, and then pass into 
the water-tubes of the gills, eventually filling up those portions 
which function as the marsupium. 
As the eggs settle down into the gills, they come into contact 
with the secretion formed by the glandular epithelium lining the 
tubes, which in many cases is of a glutinous nature, although its 
consistency varies in different species. It is, however, usually 
