MEMOIRS OF rilK NATIONAL ACADEMY OK SCIENCES. 49 



Professor W'hitiiuui" lias sIkiwm tliat in tlic lecuh the iiitcnial tissues {iMcs(il)l;i,stJ of the budding 

 zone are arranged in two widely .separated lateral hands, which, to i|U()te Wilson's exposition, 

 "as the trunk orows older widen out and yrow together alonj;- the niedian line, ulliniatcdy <;"iving 

 rise to muscles. l)lood vessels, exeretorv organs, reproductive organs, etc." Now. if this is the 

 case with the more important tissues, why in caterpillars as well as in lizards may not this opis- 

 thenogenetic mode of growth also invohe the arrangement and distribution of the pigment 

 masses of the integument ; 



\A'ithout entering into the mode of development of the germ liands, which are behind 

 completely separate, gradually Ix'coming united in front, resulting in their union or concrescence, 

 we would make the suggestion that it may be the initial cause or at least in some way connected 

 with the breaking up of the loiigituilinal stripes of the bod}', and their transformation into spots 

 at or near the budding zone of their polymerous or polypodous (Pei'i])atus-like) ancestors. 



Jn the trilobites, Limulus, and diplopods, the new segments after embioynic life are inter- 

 polated between the penultimate and anal or last segment of the liody, and it is from this 

 region in certain lepidopterous larviv that the transformation of longitudinal stripes into 

 spots takes place. The question next arises whether there is any connection between the opis- 

 thenogenetic origin of the markings of lizards and that of caterpillars. The fact now well estab- 

 lished by embryologists that the phenomena of concrescence occurs not only in tishes but in 

 Amphibia and reptiles, would suggest that the cause of the transformation of longitudinal 

 stripes into spots on the lumbar and sacral regions of lizards is the result of the same specializing 

 growth force. It may, perhaps, be regarded as a surviving remnant of the segment-forming force, 

 which has ati'ected the pigment Itands in a manner identical in the veilebratcs and insects. This 

 transformation of stripes into spots, and the fu.sion of two dorsal tubercles into a median one 

 may be then the sign of some latent or surviving amount of force concerned in the origin and 

 formation of segments, which crops out in the larval stages of insects and in young lizards, 

 resulting in this opisthenogenetic mode of origin of spots from bands. 



In this connection it will be of interest to quote some observations of Mr. Abbott H. Thayer,* 

 which bear on this subject: 



The next thing to be pointed out is^ tliat the general tendency of birdi^ to wear longitudinal markings forward, 

 and transverse ones aft, is an important factor of protection, especially in the case of the pheasants and jjeacocks, 

 among whom this arrangement is very highly developed. Any one who has tried to catch a snake in the grass will 

 see at a glance why nature tries to direct an enemy's attention behind the animal he is hunting. The snake forever 

 proves to be farther on. It is hard to set one's foot far enough ahead as he moves, just as a wing shot tends to shoot 

 behind. Now, nature realizing this, offers the enemy the utmost inducement to strike too far back. The strong 

 crossbars of the Keeves or the copper pheasant, while visually they cut the tail to pieces when it is still, are, as with 

 the peacock, by far the most visible part of the bird as soon as he moves. The reason of this is that in forward 

 motion the longitudinal markings scarcely show, while the transverse ones become conspicuous. To prove this, 

 any reader has only to blacken a few points an inch or so apart on a white cord, and then move the cord longi- 

 tudinally, drawn tight across some aperture a few yards away, the cord being only visible when it crosses the 

 aperture. He will see that its motion is distinguishable nnich farther off when the spots are in sight than when 

 the unmarked cord is passing. The spots correspond to the tail marks of the pheasant, and the ciird when it is not 

 spotted represents the bird's longitudinal markings, i. e., his body markings. 



XII. THE SUPERFAMILY SYSSPHINGINA. 



Having shown what few and really slight absolute characters separate the Sphingidiv? from 

 the Ceratocampidse; that the tw^o groups are members of a single phylum or subphyhun. i. e., 

 having evidently all descended from a common stem form, I would suggest that these facts, 

 proving blood relationship and comnuinity of origin, be emphasized by uniting the Sphingida? (or 

 Sphingoidea of Dyar) with the families grouped under the superfamily Saturnoidea (Saturniides 

 of Grote). They may be designated as the Sysyyhingina, this name indicating that the super- 



« The embryology of Clepsine. Quart. Journ. Micr. Sc. XVIII. 1878. Journal of Morphology, Boston. 1887. 

 I am indebted to Prof. A. D. Mead for calling my attention to the concrescence process in this connection. 

 ^ Trans. Entomological Soc. London, 1903, j). 569. 



