918 



SCIENCE 



[N. S. Vol. XXVII. No. 702 



supply of oxygen from the vascular system 

 of the plants. The swamp areas inhabited 

 by this species are those densely over- 

 grown with grasses in which no other mos- 

 quito larva lives and among which no fish 

 or other enemies are found. (See Ento- 

 mological News, Vol. XIX., page 22, plates 

 3 and 4, January, 1908.) 



Note on a Trematode Parasite in a Hen's 

 Egg from Northern Minnesota: W. S. 

 NiCKEESON, University of Minnesota. 

 (Read by title.) 



A Companson hetween the Implantation 

 Stages in Dipodomys and Geomys: 

 Thomas G. Lee, University of Min- 

 nesota. 



A study of a series of early develop- 

 mental stages in Dipodomys taken previ- 

 ous to and during the process of the im- 

 plantation of the ovum shows a general 

 correspondence with the same stages in 

 Geomys as previously described by the 

 writer. 



Dipodomys is the third rodent so far 

 described in which the decidual cavity is 

 formed in the ventral portion of the 

 uterine mucosa outside of and independent 

 of the uterine lumen. Perforation of the 

 ventral portion of the uterine epithelium 

 and the extrusion of the blastocyst occurs 

 at a somewhat earlier stage of develop- 

 ment than in Geomys. Consequently, the 

 opening between the iiterine lumen and the 

 newly, formed decidual cavity is at all 

 times much smaller proportionally in 

 Dipodomys than in Geomys. The blasto- 

 cyst in Dipodomys does not become at- 

 tached to the margin of this opening as 

 is so characteristic of Geomys, but sinks 

 down into the decidual cavity. 



In both Dipodomys and Geomys there is 

 for some time a functional yolk-sac 

 placenta which is later substituted by an 

 allantoic placenta. 



The Ecological Succession of Bird Associa- 

 tions: Chas C. Adams, University of 

 Chicago. 



The breeding grounds of birds must be 

 considered as fundamental in any attempt 

 to determine their habitat relations. Those 

 species which regularly breed in the same 

 habitat form a bird association or society. 

 The succession upon Isle Royale, Lake 

 Superior, has been attempted by the study 

 of the history of the environment cor- 

 related with the character of the birds. 

 From a reef in the lake to the forested 

 island there has been a definite environ- 

 mental change ; and, correspondingly, in all 

 probability, a corresponding change in the 

 bird life. Upon the habitat preferences of 

 the present avifauna the general succes- 

 sion in the past may be roughly approxi- 

 mated. As the lake level lowered and the 

 depressions became invaded by the forest, 

 the aquatic association has been succeeded 

 by the shore and bog-forest kinds; and 

 these in turn by the birds frequenting the 

 aspenbirch-balsam or maple forest. All 

 habitats, under present conditions, tend to 

 become transformed into that of the climax 

 forest, with its avifauna or association. 

 This method of environmental interpreta- 

 tion, as a problem of succession, gives a 

 new point of view for the study of the 

 development or evolution of the avian 

 environment and the "struggle for exist- 

 ence" among birds. 



A Statistical Study of Midsummer Birds 

 of Illinois: S. A. Fqebes, University of 

 Illinois. 



This paper contains a preliminary state- 

 ment of some of the more general results 

 of a census of summer resident birds of 

 Illinois, giving the entire bird population 

 of a strip 150 feet in width and 428 miles 

 long (12 square miles), one third of this 

 area being in southern, one fourth in 

 central, and two fifths in northern, Illinois. 



