MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 49 



Professor Whitman" has shown that in the leech the internal tissues (mcsoblast) of the budding 

 zone are arranged in two widely separated lateral bands, which, to (juote Wilson's exposition, 

 "as the trunk grows older widen out and grow together along the median line, ultimately giving 

 rise to muscles, blood vessels, excretory organs, reproductive organs, etc." Now, if this is the 

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

 thenogenetic mode of growth also involve the arrangement and distril)ution of the pigment 

 masses of the integument^ 



Without entering into the mode of development of the germ bands, which are behind 

 completely separate. graduall_y becoming 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 wa}' connected 

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

 at or near the budding zone of their polymerous or polypodous (Peripatus-like) ancestors. 



In the trilobites, Limulus. and diplopods, the new segments after embroynic life are inter- 

 polated between the penultimate and anal or last segment of the bod\-. and it is from this 

 region in certain lepidopterous larva; 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 fishes but in 

 Aniphibia 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 affected the pigment bands in a manner identical in the vertebrates and insects. This 

 transformation of stripes into spots, and the fusion 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 j'oung lizards, 

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



In this connection it will be of interest to ((uote some observations of Mr. Alibott H. Thayer.* 

 which bear on this subject; 



The next thing to be pointed out is that the general tendency of birds to wear longitudinal markings forward, 

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

 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 .«nake 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 Reeves 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 « hen it crosses the 

 aperture. He will see that its motion is distinguishable much farther off when the spot.-; are in sight than when 

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

 spotted represents the bird's longitudinal markings, /. <. , his body markings. 



XII. THE SUPERFAMILY SYSSPHINGINA. 



Having shown what few and reallv slight absolute characters separate the Sphingida^ from 

 the Ceratocampidu'; that the two groups are members of a single phylum or subphylum, i. e., 

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

 proving blood relationship and connnunity of origin, be emphasized by uniting the Sphingidw (or 

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

 of Grote). They ma}' be designated as the Sy-Hxplunc/ma, this name indicating that the super- 



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

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

 ''Trans. Entomological Soc. London, 1903, \\ 569. 



