188 SCIENCE PROGRESS. 



but is repeatedly found in the wild state, generally as a 

 larva. The question naturally suggests itself, how the 

 parentage of this hybrid is known. Standfuss replies that 

 the larva, though intermediate in character, shows constant 

 differences from that of 5". bornemanni, and that the condi- 

 tions in nature for the pairing of S. spini S and 5". pavonia 

 ? are favourable, whereas those for the converse cross are 

 difficult or impossible. The males of both species emerge 

 before the females, and in regions where both occur S. 

 pavonia is out first. Hence, though the females of S. 

 bavonia are out with the males of S. spini, the converse does 

 not take place. It must be allowed that it would be well to 

 test this conclusion as to the parentage of S. hybrida by 

 experiment. The larva of .S. hybrida resembles S. pavonia 

 somewhat more than does that of S. bornemanni ; it pos- 

 sesses, however, the greasy polish of 5". spini to a greater 

 extent than the latter. The cocoon and pupa both show a 

 nearer approach to «S\ spini than do those of S. bornemanni, 

 and the same applies to the perfect insect ; in fact the 

 resemblance of both sexes to the male parent is remarkably 

 close. 



3. S. pavonia $ and S. pyri ? . This crossing pro- 

 duced hybrids which fell into two classes, a dark form 

 called by Standfuss 5". danbii, and a paler form to which he 

 gives the name S. cmilice. The latter is by far the com- 

 moner. As in former cases, if the laying is much deferred 

 after pairing, the eggs are apt to prove infertile. The larva 

 in its early stages is very like that of 5. pyri; it becomes 

 more and more like that of 5. pavonia, and finally bears a 

 close resemblance to the latter species. The cocoon is 

 intermediate ; the pupa is nearer to S. pavonia than to 5. 

 pyri. The perfect insect, except for a reduction in the 

 sexual disparity of size, is more like an enlarged S. pavonia 

 than a diminished S. pyri. In a majority of specimens some 

 of the veins were forked terminally at a greater or less dis- 

 tance from the margin of the wings. 



The males of this hybrid paired readily with the females 

 of *S". pavonia ; they were also attracted by the female hy- 

 brids, though in a less degree. The latter were, as already 



