286 Alexander Petrunkevitch 



leave her. I had, besides, several unripe specimens of unknown 

 age. I had also Phidippus in the same stages as Lycosa. It is 

 not difficult to obtain these since the female of this species make 

 a tent of web in which she lays the, eggs, afterward guarding the 

 young ones for a considerable time. I caught in addition several 

 females of Pardosa nigropalpis with young ones on the back. 



The method employed is as follows : Instead of measuring each 

 eye and the distances between the eight eyes in each spider, I make 

 with the aid of the Abbe apparatus a drawingof theentireeye-group 

 of an adult female. Leaving the drawing in the same position 

 on the drawing table, I remove the adult female and substitute a 

 younger one. I then try different objectives and oculars .until 

 the image on the paper of the eye-group of the younger spider is 

 of the same size as the drawing of the adult. A sheet ot clean 

 paper is now put in place of the one with the drawing and the new 

 drawing is made. In this way drawings are obtained of all 

 stages. The angles of the eye-axes are next measured and the 

 axes drawn in on the corresponding figures. In all cases, begin- 

 ning with the young spider at the time when it is ready to leave 

 the mother in order to commence its own, independent existence 

 and ending with the mother herself, the configuration of the eye- 

 group and the angles of the axes proved to be the same and the 

 drawings made of them on paper, when superposed and examined 

 against the light, coincide absolutely. But this does not apply 

 to the youngest spiderlings, those taken directly out of the cocoon. 

 Although in such spiderlings the eye-group is in general very 

 nearly the same as in the adults, careful measurements show dif- 

 ferences which, while not appreciable to the unaided human eye, 

 are nevertheless of great importance. I give these measurements 

 here (Table IV) but shall discuss them farther on when exam- 

 ination of the fields of vision will reveal more clearly their 

 significance. It is unfortunately still more difficult to measure 

 the angles in such spiders than it is in older ones so I give only 

 figures of which I am certain. 



If we compare these tables with those for the adult females 

 we shall at once notice the following differences. In the youngest 

 spiderlmgs of Phiddippus and Lycosa the anterior middle eyes 



