l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 143 



the caterpillars. Hinton ( 1955) gives a good account of the mechanism 

 of the planta that operates the crochets. Only a few special examples 

 will be given here. 



Prolegs typical of climbing caterpillars are well shown by the 

 tomatoworm Protoparce quinquefasciata (fig. 9 A). The mesal part 

 of the planta projects as a pad, which, when viewed ventrally (C), 

 appears to be armed with a marginal row of larger upturned hooks and 

 a submarginal row of smaller hooks. On the mesal surface of the 

 pad (D) it is seen that each hook is supported on what appears to be 

 a slender vertical bar in the wall of the planta. Dissection reveals, 

 however, that these apparent bars are the exposed edges of the crochets 

 themselves (F) which are deeply buried in grooves of the plantar 

 surface, and that the visible hooks are only their free outer ends. The 

 wide bases of the crochets are articulated by mesal points (F, a) in an 

 even row on the plantar lobe (D). The same type of plantar structure 

 is seen in the silkworm (G, H). 



In the resting caterpillar clinging to a twig, the prolegs are kept 

 extended by internal body pressure, or turgor; the crochet-bearing 

 pads are then turned mesally and the claws firmly grasp the support 

 (fig. 9 B). The retractor muscle of the planta is attached laterad of 

 the base of the crochet-bearing lobe, and, as noted by Hinton (1955), 

 a contraction of the muscle turns the lobe downward and disengages 

 the claws. When the caterpillar is crawling, the plantae are succes- 

 sively lifted to allow the prolegs to be carried forward with the exten- 

 sion of their segments. 



On flat surfaces or on the ground the crochets probably have little 

 use, the prolegs serving merely as supports for the abdomen. The 

 actively running arctiid caterpillars have very short prolegs (fig. 9 J). 

 In the yellow woolybear Diacrisia virginica (fig. 9 1), the crochet- 

 bearing lobe is crescent shaped with a single row of marginal upturned 

 crochets. Some caterpillars are able to walk on glass by pressing the 

 plantae flat against the surface. Presumably a slight contraction of 

 the plantar muscles converts the feet into suction cups. Such cater- 

 pillars can adhere to the glass at a steep angle, but they cannot crawl 

 on a vertical glass surface. Probably they maintain a foothold in the 

 same way on the surface of leaves. 



A different type of planta is seen in a stem-boring larva of Hepiahts 

 (fig. 6 F). The short median prolegs (fig. 9 K) end with flat plantar 

 surfaces (L), each bearing a transverse oval series of larger crochets 

 surrounded by an outer series of small crochets. The plantar muscle 

 is attached excentrically on the plantar surface. The anal prolegs have 

 each a pair of plantar discs side by side (M), with crochets only on 



