]SJ"o. 3. — OhservatioTis on the Development of Agelena ncevia. — 



By Wm. a. Locy.* 



Several memoirs have been published on the development of the 

 Araneina, but the residts attained are still unsatisfactory on account of 

 the disagreement of authorities, and the limited extent to which the 

 method of sectioning has been employed in studying the subject. Up to 

 the present time only a single memoir, illustrated by figures of actual 

 sections, has appeared. 



Valuable as were the works of the earlier writers, Herold ('24), Eathke 

 ('42), and Von Wittich ('45 and '49), they now are principally of his- 

 torical importance, since their labors were performed either before the 

 announcement of the cell theory, or before it had gained general recog- 

 nition, and before embryology had attained its pre-eminence among mor- 

 phological studies. 



Claparede ('62) made extended observations on the external features 

 of development, but did not discuss the preblastodermic period nor the 

 period of the revolution of the embryo. 



Salensky ('71) published in Eussian a memoir, the figures illustrating 

 which show critical observations on the external features of development. 

 He was the first to figure the " rudimentary terga " of the period of revo- 

 lution, and also the development of the procephalic lobes. 



In a short paper on the development of Pholcus, Emerton ('72) con- 

 fines his observations to the external features of development. He figures 

 the polygonal areas of the blastema, and erroneously concludes that they 

 are blastodermic cells without distinct nuclei. The relation of the primi- 

 tive cumulus to the ventral plate is well figured. 



Balbiani ('73) has produced one of the most satisfactory memoirs yet 

 written ; he figures and describes in detail the external features of the 

 early stages of development up to the period of the formation of the 

 appendages. 



Ludwig's ('76) observations were confined to the formation of the blas- 

 toderm, and are at variance with Balbiani's, mainly in denying the exist- 



* Contributions from the Embrvological Laboratory of the Museum of Com- 

 parative Zoology at Harvard College, under the direction of E. L. Mark. No. VIII. 



VOL. XII. — NO. 3. 



