PROBABLE DIMORPHISM OF THE EGGS OF AN 



ARANEAD. 1 



THOS. H. MONTGOMERY, JR. 



On comparing the eggs from cocoons raised in captivity of the 

 common spider, Theridinui tepidariorum, C. K., 2 I was struck by 

 the fact that eggs of the same age but from different cocoons 

 may be of distinctly different volumes. That is to say, all the 

 eggs of one cocoon may be larger or smaller than all the eggs 

 of another cocoon made by the same spider. 



In this comparison only such egg batches were considered, of 

 which I had records as to the exact hour of oviposition. Further, 

 comparisons were made only of eggs preserved by the same fix- 

 ative, hardened in the same way, and preserved in the same 

 grade of alcohol ; in all cases the cocoons were opened and the 

 eggs dropped into the fixative. Then all the spiders came from 

 one locality, and all lived under the same conditions of captivity 

 in the month of August, 1906. 



The following cases exhibited different volumes of the eggs of 

 successive cocoons made by particular spider individuals : 



1S3. 



i. One spider formed three successive cocoons, nos. 752 (pth 

 August), 818 (Hth August), and 872 (igth August). Every 

 egg of no. 752 (fixed at the age of twelve hours) was markedly 

 larger than any egg of no. 818 (fixed at the age of fifteen hours) 

 and no. 872 (fixed at the age of nineteen hours). The difference 

 in these egg sizes is shown in the accompanying figures. 



Contributions from the Zoological Laboratory of the University of Texas, no. Si. 

 ^Vide ray preceding paper in this journal, "The Oviposition, Cocooning and 

 Hatching of an Aranead, Theridium tepidariorum, C. Koch." 



"5 



