46 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



spots, and have the supraspiracular and subspiracular areas bluish or 

 bluish-white. The absence of a dorsal stripe is probably due to a lack 

 of any cement layer being deposited, since most specimens have no 

 stripe, but a few specimens may show a weak dorsal stripe. The orange 

 color, so prominent in forms such as M. californicum pluviale, is only 

 slightly developed and shows merely as a few irregular longitudinal 

 orange lines. The anterior and posterior subdorsal spots are greatly 

 reduced or even absent. The vertical black bar is obscured by the 

 predominance of black in the surrounding areas, but a few lighter 

 individuals clearly show the vertical black bar as a distinct area. 

 These lighter individuals also have a more distinct dorsal stripe, more 

 conspicuous orange areas, and larger anterior and posterior subdorsal 

 spots. All of these characteristics are tending toward those of some 

 populations of californicum found north of San Francisco Bay, and help 

 confirm c. ambisimile's status as a subspecies. 



Sexing Larvae 



Larvae of Malacosoma are easily sexed by characters found on the 

 venter of the ninth abdominal segment of males and on the eighth 

 and ninth abdominal segments of females. Males have a very small 

 pit or depression midventrally near the anterior edge of the ninth 

 segment (fig. 79). This pit marks the location of an internal histoblast 

 which is connected by the vas deferens to the testes which are located 

 on either side of the fifth segment. 



Females have two pairs of slightly larger and more conspicuous 

 pits, one pair on the eighth and one pair on the ninth segments (fig. 

 80). These pits mark the location of internal histo blasts which no 

 doubt represent part of the genital system. The lateral oviducts, which 

 leave the ovaries in the fifth segment, converge and join together 

 ventrally about midway through the seventh segment without making 

 any obvious connection with either pair of histoblasts, or with the 

 integument of the seventh segment. If there is a connection between 

 the histoblasts and the oviducts at this stage of development, it is very 

 delicate and could not be dissected out in the specimens at hand. 



These pits are present in all instars of both males and females, but 

 the smaller the larva, the more difficult the pits are to see, especially 

 if the ground color of the integument is light. The most positive way of 

 sexing them is to look for the presence or absence of the four pits of 

 females since the pit on the males is quite small and easily overlooked 

 on some specimens. Last instar specimens can usually be easily sexed 



