100 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



in fact the vitelline membrane, and deliverance therefrom constitutes the 

 first moult. 



The number of times that spiders change their skin before they be- 

 come adult is not uniformly the same as regards ever}' species, not even 



perhaps the same within the individuals of any one species. 

 Periodic- p or exam pi e) Blackwall made some careful observations upon the 

 -7 ,,. frequency of moulting in a young female of Zilla x-notata 1 and 



Epeira diademata, which I arrange for sake of comparison in 

 the following tabulated form : 



XlLI.A X-NOTATA. El'EIItA KIADEMATA. 



Days Interval. Days Interval. 



Disengaged from egg March 30th, April 14th, 



1. Moulted in cocoon April 8th, 9 April 24th, 10 



Quitted cocoon May 1st, May 3d, 



2. Moulted June 4th, 54- 



3. Moulted June 22d, 18 June 21st, 50 2 



4. Moulted July 12th, 20 July 10th, 19 



5. Moulted August 4th, 23 August 3d, 24 



There were five moults in each case ; the intervals between disengage- 

 ment from the egg and the first moult were about the same ; the Epeira 

 remained much longer in the cocoon than the Zilla, perhaps for some local 

 reason; its next moult, the first after emerging, was not recorded. But 

 there was evidently an irregularity during the interval from moult 1 to 

 moult 3 where the record can again be compared. However, if we take 

 up the comparison from the dates of leaving the cocoons, the moulting 

 intervals of the two species are of nearly equal length. Perhaps this table 

 represents fairly enough the normal periodicity of moulting with Orb- 

 weavers. 



With Lycosids (Trochosa), according to Wagner, the second skin is 

 rejected in about six days, at a time when the younglings dwell in part 

 within the cocoon and partly on the mother's back. The third 

 T y< 3 ' moulting occurs six to seven days thereafter upon the mother's 

 ' body. The fourth moult occurs seven to eight days after the 

 third, partly on the mother's body and partly in the maternal burrow. 

 After this moult the younglings leave the burrow and begin independent 

 life. At this time the spiderlings have attained more than one-tenth their 

 normal size, and have before them a series of moults amounting to ten in 

 all. 3 The time required for full development and for completion of all the 

 moults is from one hundred and sixty to one hundred and ninety-five 

 days, excluding winter months. 



The periodicity and the safety of moulting are modified by various 



1 Epeira calophylla Blackw. 



2 There is probably a break here in the observation, and a loss of several moults. 



3 Wagner, Note on the Tarentula, Comtes rendus de la Sect. Zool. de la Soc. Imp. des 

 Sc. Nat. de Moscow, 1866. 



