April 4, 1902.] 



SCIENCE. 



529 



Important parts of the mid, 'tween and 

 fore brain (inferior lobes, central gray,- 

 striatum [ ?], etc.) belong to the same cate- 

 gory as the tract and commissural cells of 

 the medulla and cord. The nucleus of the 

 posterior commissure and the olfactory 

 apparatus cannot be compared with any 

 structures in the cord or hind brain. There 

 is no essential resemblance between the 

 olfactory nerve and its central apparatus 

 and the typical cranial nerves and their 

 centers. The olfactory nerve has no seg- 

 mental value. 



The Development of the Postcaval Vein in 

 Didelphys Virginiana: C. F. W. Mc- 

 Clure. 



The variations in the mode of origin of 

 the postcaval vein of the common opossum 

 are so extreme as to preclude our formu- 

 lating a typical arrangement for the spe- 

 cies as a whole. .The different modes of 

 origin which characterize the postcaval 

 vein in the adult are briefly as follows : 



1. The postcaval vein may be formed 

 through a union of the iliac veins which 

 takes place ventral of the common iliac 

 arteries (type I.) ; 



2. Through a union of the iliac veins 

 which takes place dorsal of the common 

 iliac arteries (type II.) ; or, 



3. Through a union of the iliac veins 

 which takes place both dorsal and ventral 

 of the arteries in question (type III.). 



A study of the embryonic development 

 of the posterior tributaries of the postcava 

 shows, I think, how these variations have 

 been derived. Embryos of 8.5, 12, 1.5 and 

 22 millimeters in length were examined. 



In an embryo 8.5 millimeters in length 

 the umbilical artery, on each side, passed 

 through a complete foramen in the post- 

 cardinal vein, so that one portion of the 

 circumarterial venous ring lay ventral and 

 another dorsal of the artery. This fora- 

 men was situated near the point of union 



of the external and internal iliac veins. 

 In a subsequent stage the internal iliae 

 veins approached each other in the median 

 line and fused ventral of the caudal artery 

 to form a common internal iliac vein. 



The writer believes that the type of post- 

 caval vein to be assumed by the adult 

 depends upon the loss or persistence of 

 those portions of the circumarterial venous 

 rings which lie dorsal and ventral of the 

 umbilical arteries. 



If the atrophy affects the dorsal 

 branches of the circumarterial venous 

 rings, a postcava will result as in type I. 

 If it is the ventral branches of the rings 

 that atrophy, a postcava will result as in 

 type II., but, if dorsal and ventral 

 branches of the rings both persist, a post- 

 cava of type III. ^vill be formed. 



The Development of Pigmental Color in 

 Insects: W. L. Tov^er. (Read by title 

 only.) 



Progressive Variation in a Given Genera- 

 tion of some Plants and Animals: W. L. 

 Tower. (Read by title only.) 



Observations on the Habits of Hyalella 

 dentaia Smith : Samuel J. Holmes. 

 The observations on Hyalella that were 

 made related to food habits, thigmotaxis, 

 phototaxis, reactions to pressure and sexual 

 habits. Experiments were performed with 

 the end of determining the mode of sex 

 recognition in Hyalella. That sight plays 

 no important part in the process was proved 

 by the fact that males whose eyes were 

 blackened over with asphalt varnish suc- 

 ceeded as well as others in obtaining fe- 

 males. Neither did removal of the first and 

 second pairs of antennse in the males pre- 

 vent their obtaining mates. It is therefore 

 improbable that the males are guided 

 to the females by the sense of smell. Sev- 

 eral females, some of which were recently 

 torn from males, were placed within a 



