230 



SCIENCE. 



[N. S. Vol. V. No. 110. 



both of which are further subdivided into beds 

 characterized by certain leading fossils. The 

 Maquoketa series is divided into the Transition, 

 Maquoketa and Wykoff formations, which also 

 comprise beds marked by the presence of cer- 

 tain genera. 



Jules Marcou has the first installment of a 

 paper on ' Rules and Misrules in Stratigraphic 

 Classification.' The early history of geologic 

 correlation is sketched, and the independent 

 discoveries of Giraud-Soulavie, William Smith, 

 Cuvier and Brongniart are reviewed. Direct 

 application is then made to American geolog- 

 ical correlation, with special reference to the 

 Taconic and Ohamplain systems. 



' The relation of the streams in the neighbor- 

 borhood of Philadelphia to the Bryn Mawr 

 gravel,' by F. Bascom. With the exception of 

 the large rivers, the streams of this region are 

 shown to be of superimposed origin, having 

 begun on a surface covered with gravel deposits, 

 underlying which were older crystalline and 

 paleozoic rocks. This has made their valleys 

 quite independent of the strike or hardness of 

 the rocks through which they are now cutting. 

 The age of the Bryn Mawr gravels has been 

 uncertain, and they have been referred to the 

 Mesozoic, the Tertiary and the Quaternary by 

 various observers. The author shows that they 

 cannot belong to the Quaternary and inclines 

 to the belief that they are a member of the 

 Potomac formation, though the data obtained 

 from the study of the drainage system may not 

 be sufliciently exact to precisely determine their 

 geologic relations. 



SOCIETIES AND ACADESIIES. 



ZOOLOGICAL CLUB, UNIVERSITY OP CHICAGO, 



MEETING OF JANUARY 6, 1897. 



ABSTRACTS OF PAPERS PRESENTED. 



I. MICROSOMES AND THEIR RELATION TO THE 



CENTROSOME. 



The problem of the centrosome presents it- 

 self under five heads : 



1. The centrosome in caryokinesis of tissue 

 cells. 



2. The centrosome in the maturation of the 

 ovum. 



3. The centrosome in fecundation, or, more 



strictly, the problem of the origin of the centro- 

 somes which take part in the first caryokinetic di- 

 vision of the fertilized egg-cell. 



4. The centrosome in cells in which locomo- 

 tor function is more or less well developed, as 

 in leucocytes, pigment-cells, and some unicel- 

 lular organisms. 



5. The centrosome in some cells which un- 

 dergo periodic growth, as in the sperm-mother- 

 cell, the ovarian ovum, and some tissue cells. 

 The centrosome in some ganglion cells probably 

 belongs to this group of phenomena. 



It was pointed out that these are co- 

 ordinate features of one and the same problem. 

 The different forms of the centrosome and their 

 mode of origin, their variations under patho- 

 logical conditions, their behavior during fer- 

 tilization of the ovum in different forms, were 

 examined in reference to two fundamentally 

 opposed theories now current among cytolo- 

 gists. 



In this connection a historical review of our 

 knowledge of the microsomes (cytomicrosomes), 

 as found in the observations of Hanstein, 

 Schmitz, Schwartz, Strasburger, van Beneden, 

 Boveri, Heidenhain, together with the author's 

 observations on the ovarian ovum of an as- 

 cidian, was presented, and the bearing of the 

 microsome question on the problem of the cen- 

 trosome, pointing to the existence of homol- 

 ogy between microsome and centrosome, was- 

 indicated. 



The main conclusion of the paper was as fol- 

 lows : The living substance of the cell-body 

 is to be regarded as composed of an element 

 capable of dimorphic existence, with perfect 

 freedom of transition from one to the other, 

 under some definite condition. It can exist in 

 the form of cytomicrosomes, or it can assume 

 the appearance of clear, hyaline filaments, net- 

 work, or vesicular structure, as the case may be. 

 At one stage, the cell-body of a given cell, say 

 an ovarian ovum of some organism, may be 

 composed almost wholly of microsomes ; at the 

 next these microsomes may be transformed 

 into hyaline cytoplasmic substance, with cor- 

 responding increase in the bulk of the cell. 



In the phenomena of caryokinesis, fecunda- 

 tion, motion, periodic growth of the cell re- 

 ferred to at the beginning of the paper, both of 



