582 



SCIENCE. 



[N. S. Vol. XV. No. 380. 



two sides are symmetrical, but in the posi- 

 tion, distribution, number and minor de- 

 tails of the branches from the ' lateral ' 

 and 'main ' canals there is considerable 

 variation. In none of the several hundred 

 specimens examined were these branches 

 grouped as described and figured by Col- 

 linge. In all cases they were found all 

 along the ' lateral ' canal, the great ma- 

 jority being ventral to the canal. As a 

 rule, one to three at the anterior end of 

 each system begin on the ventral side of 

 the canal and, after running a short dis- 

 tance in that direction, turn dorsalward 

 and terminate in the usual branchlets and 

 clusters of sense organs on the dorsal side 

 of the canal. 



The points made were demonstrated 

 with dried skins of the fish upon which the 

 systems had been painted over with white 

 paint, and photographs of similarly pre- 

 pared skins. 



Conditions of Fossilization: J. Culver 

 Hartzell. (Read by title only.) 

 Professor Hartzell 's paper was a review 

 of a series of investigations he has been 

 making, the objective point of which is to 

 find the laws ( 1 ) governing the conditions 

 of fossilization for the various classes of 

 Invertebrates in the same and in different 

 formations. 



Before the laws desired can be formu- 

 lated, it is necessary (a) to know the min- 

 eral composition of the skeletal parts of 

 living invertebrates; (&) to know the con- 

 dition of the fossil, i. e., whether it be the 

 original, a mold or a cast; (c) to know 

 the mineral composition of the fossil; (cZ) 

 to know what mineral change has taken 

 place during fossilization where the cast 

 is one by molecular replacement; (e) to 

 knoAV the lithological composition of the 

 formations in which fossils occur; (/) to 

 know the relationship between the fossil 

 and the formation. 



The conversion of an organism into a 

 fossil depends upon the character of its 

 skeletal parts, the material in which it is 

 buried and the material brought in in solu- 

 tion by infiltration. The material of which 

 the skeletal parts is composed varies in 

 diiferent groups, being more durable in 

 some than in others and therefore plays 

 an important part in the preservation of 

 the organism. The variation in the litho- 

 logical character of the material in which 

 the organism is buried also plays an im- 

 portant part. Certain organisms are pre- 

 served as originals, others as molds and 

 casts, in the same formation, and locality. 

 In this same formation, but in a locality 

 of different lithological character, those 

 groups which were lost under the former 

 condition may be retained under the latter, 

 and vice versa. 



So far, twenty-five horizons and forty- 

 four localities in the United States, Can- 

 ada, England and Germany have been ex- 

 amined with special reference to the litho- 

 logical character of each formation at the 

 various localities and the conditions of 

 preservation of the fossils. Tables have 

 been prepared giving the general mineral 

 character of the skeletal parts of living in- 

 vertebrates, minerals replacing original 

 minerals secreted by the organisms, and a 

 comparative table showing the mineral 

 composition of living and fossil inverte- 

 brates. 



The paper was illustrated by means of 

 photographs, drawings and models. 



Origin and Migration of the Germ-Cells 

 in Squalus Acanthias: Frederick Adams 

 Woods. 



The germ-cells in this form are not de- 

 rived from the germinal epithelium of 

 the body cavity, as is commonly taught, 

 but are traceable before the mesoderm has 

 split to form the coelom, and in a region 

 that may be called extra-embryonic. 



