16 Journal of the Mitchell Society [August 



Some Phases of Digestion in Cambarus. William A. Wolff. 



I, Carbohydrates. Caniharus takes and digests carbohydrate 

 food.. Enzyme extract from both intestinal and liver tissue digested 

 starch and maltose, sucrose in some instances, but not lactose. Amy- 

 lase and maltase were found in the intestine ; sucrase and lactase were 

 absent. In the liver amylase, maltase, and traces of sucrase were 

 found, but lactase was absent. 



Twinning and Pohjemhryonij in Insects. R. W. Letby. 



In the polyembryonic development of some of the parasitic insects 

 as many as 160 to 2500 individuals are developed from a single egg 

 deposited by the parent parasite in the egg of the host. The develop- 

 ment of the parasites is completed in the larval stage of the host. 



In the case of Platygaster hiemalis, a parasite of the Hessian Fly, 

 a group of four to eight eggs is deposited in the egg of the fly. Some 

 of the eggs of the group develop monembryonically, while other eggs 

 of the same group develop tAvins. The cleavage nucleus divides once 

 while located in a differentiated embryonic region of the egg. The 

 two daughter nuclei then divide to form four embryonic nuclei. In 

 the case of an egg that is destined to produce twins, the embryonic 

 region of the egg divides at this stage, two of the embryonic nuclei 

 passing to one embryonic region and the other two nuclei to the second 

 embryonic region. Each embryonic region with its component em- 

 bryonic nuclei and paranuclear masses finally develops into a parasite 

 larva, and then into an adult parasite. The process of development 

 of twins is identical with that of a single individual, except that in the 

 former instance the embryonic region divides at the 4-cell stage, while 

 in the latter instance it fails to divide at the 4-cell stage. Approxi- 

 mately eight parasites develop in a single host larva. 



The twinning development of this insect is the first specialized step 

 from monembryony to polyembryony. 



The Relation of Diet to the Developynent and Preservation of the 

 Teeth. F. AV. Sherwood. 



A review with especial emphasis on the work of McCollum and of 

 Howe. 



The former has shown that when rats are fed diets which contain 

 a faulty calcium : phosphorus : organic factor ratio marked dental 

 defects result. 



