576 



SGIENGE. 



[N. S. Vol. VII. No. 173. 



ZOOLOGICAL CLUB, UNIVERSITY OF CHICAGO — 

 FBBRUAEY AND MARCH, 1898. 



THE PRONEPHROS IN TESTUDINATA. 



WiEDERSHEiM, in his paper, ' IJber die Ent- 

 wicklung des Urogenital apparates bei Crocodi- 

 len und Schildkroten,' 1890, states that he has 

 been entirelj' unable to distinguish between 

 pronephros and mesonephros. A study of the 

 earlier developnaent explains his position. 



From some very young embryos of Aromo- 

 chelj's and Platypeltis it has been possible to 

 determine the origin and extent of the prone- 

 phros. It arises as segmental outgrowths from 

 the posterior somatic region of the somites and 

 is very marked, bridging over the fissure from 

 one somite to the next. The tips overlap and 

 fuse with the following outgrowth. In a very 

 young series the fusion is so complete that a 

 prominent and quite even ridge or welt is 

 formed, extending from the sixth to the tenth 

 somite. Stretching from the end of the prone- 

 phros we find the pronephric duct at first close 

 to the somites, further back free, and at its tip 

 at least in some cases fused with the ectoderm. 

 Mitsukuri says he has proved this fusion beyond 

 the possibility of a doubt. 



As we proceed to the later stages, however 

 a new factor comes in which greatly modifies 

 these conditions. Before there is more than a 

 hint of the lumen in the pronephric tubules; 

 we see in some of the same somites (from the 

 second pronephric tubule, on) as well as further 

 back, at the point where they pass in the mid- 

 dle plate, a thickening and occasionally a small 

 bubble-like lumen. These are the Anlagen of 

 the mesonephric tubules. They become more 

 and more distinct. In some series we find the 

 funnel of the pronephric tubule and that of this 

 mesonephric I'udiment, opening side by side 

 into the body cavity, but further posterior, and 

 in older embryos we find the pronephric funnels 

 opening into these rudiments of the mesone- 

 phros and through them into the body cavity. 



There is no break between the pronephros 

 and mesonephros. The first purely mesone- 

 phric tubule is in the next somite to the last 

 one which shows the fusion of pronephric and 

 mesonephric elements. Thus it becomes clear 

 that although the pronephros is distinct in 



origin, it arises as segmental outgrowths from 

 the somites and extends over but few segments \ 

 the mesonephros arising from the middle plate 

 extends almost as far anterior as the pronephros, 

 and the two are so fused in the later stages that 

 the parts cannot be distinguished without a 

 study of their development. 



The glomus is not seen in any of the stages 

 described, except as a cluster of cells resembling 

 blood corpuscles may be very rarely found 

 alongside of the aorta. Its origin and develop^ 

 ment will be discussed later with the further 

 development of the excretory system. 



E. R. Gregory. 



Titles of other papers read during the two 

 months : ' The Maturation, Fertilization and 

 Early Cleavage of Myzostoma,' Dr. W. M. 

 Wheeler ; ' The Germinal Vesicle iu Amphibia ' 

 (Carnoy), F. L. Charles ; ' Dr. Mead on Annelid 

 Cytogeny,' W. L. Tread well ; 'The Stage of 

 Synapsis in the Squid-egg,' Miss M. M. Sturges; 

 ' The Photospheria of Nyctiphanes with Re- 

 marks on the Origin of Luminous Organs,' Dr. 

 S. Watase ; ' A Comparative Study of Cell Lin- 

 eage,' S. J. Holmes ; ' Notes on a new Peripatus 

 from Mexico, ' Dr. W. M. Wheeler ; ' A New 

 Pigeon Hybrid, ' Dr. C. O. Whitman ; ' Carnoy 

 on the Fertilization of Ascaris, ' W. H. Packard. 



NEW BOOKS. 

 Fossil Plants. A. C. Seward. Cambridge, 



The University Press. 1898. Vol. I. Pp. 



xviii + 452. 12s. 

 A Text-Book of Botany. E. Steasburger, F. 



Noll, H. Schenck, A. F. W. Schimper ; 



translated from the German by H. C. Porter, 



Ph.D. London and jNew York, The Mac- 



millan Company. 1898. Pp. ix-f 632. $4.50. 

 Methods for the Analysis of Ores, Pig Iron and 



Steel. Easton, Pa., Chemical Publishing Co. 



1898. Pp. 130. Paper, 75c.; cloth, $1.00. 

 Tlie Meaning of Education and other Essays and 



Addresses. Nicholas Murray Butler. 



New York and London, The Macmillan Co. 



1898. Ppxi-f230. $1.00. 



Erratum : On page 468, lines 10 and 11 from the 

 bottom of column 1 the words neuxite and dendrite 

 should be transferred. 



