228 



SCIENCE. 



[N. S. Vol. VII. No. 164. 



ance in the neural tube: A transitory set 

 that arise in connection with the original 

 optic differentiation, and which completely 

 disappear before the second set or true 

 brain vesicles arise. The lateral expan- 

 sions of the neural tube which constitute 

 the beginning of the eye vesicles are elon- 

 gated, and they are converted into the true 

 optic vesicles in front and a succession of 

 similar but smaller ones which are serially 

 arranged behind the former. The latter 

 series, which consists of six pairs of ves- 

 icles, is very transitory, passing through 

 the stages of rise, culmination and decline 

 within three or four hours' time. 



The structures occur in normal embryos. 

 Five hundred eggs were incubated and fifty 

 embryos obtained at the right ages to show 

 the history of these structures. They were 

 studied in living specimens in warm salt 

 solution. The observations were originally 

 made in 1893 and verified and reverified in 

 a variety of ways since that time. The 



. specimens were sketched, photographed, 

 sectioned and, in some cases, reconstructed. 

 By placing the specimens under a dissect- 

 ing microscope, where several can be viewed 

 at the same time, and making a critical 

 comparative study of all the embryos, they 

 may be arranged in a graded series, the 

 extremes of which differ considerably, but 

 the intermediate embryos show slight gra- 

 dations. In such a series it is observed 

 that these vesicles do not, in any case, de- 

 velop progressively to become brain ves- 

 icles, but undergo decline before the brain 

 vesicles appear. At their period of great- 

 est development — between the 24th and 

 26th hour, with six somites — there are six 



, pairs ; they are reduced during the next 

 hour to four pairs, and, at about the 27th 

 hour, with eight somites, they are reduced 



, to two, which rapidly fade away. From 

 this period the true brain vesicles begin to 

 appear. The author's observations on the 



- development of the brain vesicles agree 



with those of Duval, Piatt and other ob- 

 servers. It was shown that the first set of 

 vesicles are independent of the brain ves- 

 icles and have not before been figured. 



The theoretical bearing of the facts is 

 obvious, and, although the author desig- 

 nates these structures ' accessory optic 

 vesicles,' from their connection with the 

 original optic differentiation and from their 

 resemblance to the primary optic vesicles, 

 nevertheless he holds this view in the light- 

 est way, ready to withdraw it whenever any 

 better interpretation may be presented. 

 The validity of the facts is held to be estab- 

 lished, and their history has been carefully 

 worked out. Demonstrations of these struc- 

 tures to those interested followed. 



The Thoraeie Derivatives of the Post- cardinal 

 Veins in Swine. G. H. Paeker. 

 Embeyonic pigs of about six millimeters 

 greatest length possess well developed right 

 and left post-cardinals (posterior cardinal 

 veins) which extend from the base of the 

 corresponding posterior extremities anterior- 

 ly over the dorsal surfaces of the Wolf&an 

 bodies to the region of the heart. The 

 thoracic portion of each post-cardinal per- 

 sists from the region of the heart to the 

 tenth pair of ribs, beyond which a new 

 vessel, the accessory vein, is developed, 

 reaching to a point some distance posterior 

 to the last pair of ribs. The combination 

 of the post-cardinal and accessory vein ot 

 the right side gives rise to the azygos vein ; 

 the corresponding veins of the left side pro- 

 duce the hemiazygos. The axygos and 

 hemiazygos veins receive the intercostal 

 veins of their respective sides, and become 

 mutually connected by several transverse 

 veins. In later embryonic life the cardinal 

 portion of the azygos vein usually degen- 

 erates completely, and the right intercostal 

 veins connected with this part find outlets 

 through the corresponding part of the hemi- 

 azygos which persists in the adult pig. The 



