THE LIFE OF THE SPIDER 45 



madagascariensis; and I have discovered that the male of Mastophora 

 cornigera undergoes only two molts before becoming mature. 



Even within the same species there is variation in the number of 

 molts. Bonnet found that to become mature, females of Dolomedes 

 plantarius molted as few as nine or as many as thirteen times. The 

 number of molts was to some extent correlated with size, the larger 

 examples requiring more molts, but various other factors were im- 

 portant, the amount of nourishment being one. The males of this 

 same species became adults after nine, ten, or eleven molts, a number 

 similar in the lower limits to that of the female that they resembled 

 in size. In the northern United States the egg sacs of the species of 

 Mastophora are broken open early in the spring and the young 

 disperse. The males emerge either in the penultimate stadium or 

 fully mature, in the latter case having molted only twice. The fe- 

 males are of the same size, and presumably have likewise undergone 

 one or two molts, but they must molt seven or eight times before 

 they are sexually adult. The difference between molts is probably 

 five or six, and reflects an enormous disparity between the size of 

 the sexes, a difference greater than in any other spiders known to 

 me. Time is also important, and whenever maturity is reached 

 quickly for the species, the molts are near the minimum for the 

 species. When maturity is retarded for some reason, more molts 

 are undergone. Abundant food diminishes the number of molts, 

 whereas starving increases the number. 



For very few North American spiders is the number of molts 

 known. The black widow, Latrodectus mactans, has been studied 

 rather carefully by several investigators, and we find the usual con- 

 siderable differences between the sexes as regards molting behavior. 

 The males become adult after the fifth, sixth, or seventh molt, 

 whereas females are adult after the seventh, eighth, or ninth molt. 

 In the related spider Teutana grossa the males become adult at the 

 sixth or seventh, the females at the seventh or eighth molt. This 

 number of molts is about average for spiders of this general size, and 

 the males almost invariably molt at least one less time than the fe- 

 male. In 1927 Gabritschevsky recorded the time intervals between 

 molts for Misumena vatia as a part of his paper on the change in 

 pigmentation of that species. The synopsis is as follows: Deposition 

 of eggs, July 28; hatching, August 8 (my estimate); first molt, about 

 August 12; emergence from the egg sac, August 14; second molt, 

 August 24; third molt, September 5; fourth molt, September 23; 



