186 SCIENCE PROGRESS. 



fuss remarks that the absence of uniformity in the results 

 shows that several trials should be made before any given 

 cross is pronounced infertile. 



Five crosses are mentioned from which only male off- 

 spring are known to have resulted ; these are Deilephila 

 porcellus L. $ and D. elpenor L. ? ; Smerinthus austauti 

 Stgr. $ and 6". atlanticus L. ? ; Fumea nitidella Hof. $ 

 and F. affinis Rutt. ? , with the reciprocal cross F. affi?iis 

 & and F. nitidella ? ; Bombyx neustria L. $ and B. fran- 

 conica Esp. ? . 



In the following five cases only female offspring have 

 been observed, and these contained no eggs capable of de- 

 velopment : Bombyx neustria L. $ and B. castrensis var. 

 veneta Stdfs. ? ; B. franconica Esp. $ and B. castrensis 

 var. veneta ? ; B. quercus L. $ and B. trifolii Esp. ? ; 

 Saturnia pyri Schiff <$ and 6". pavonia L. ? ; Drepana 

 curvatula Bkh. $ and D. falcataria L. ? . 



In the following seven the males predominate and the 

 females are again sterile : Deilephila euphorbia L. 8 and 

 D. vespertilio Esp. ? ; D. hippophaes Esp. $ and D. 

 vespertilio Esp. ? ; Smerinthus ocellatus L. S and .S. populi 

 L. ? ; Saturnia spini Schiff $ and 6". pyri Schiff ? ; S. 

 spiui Schiff S and S. pavonia L. ? ; Harpyia vinula L. $ 

 and H. erminea Esp. ? ; Notodonta dromedaria L. $ and 

 N. torva Hb. ?. 



The author points out that no fertile female offspring 

 having been observed in any of the above seventeen crosses, 

 none of these hybrids, so far as our present knowledge goes, 

 could continue their race. It is unfortunate that the actual 

 numbers of the broods in question are not given ; in some 

 instances, as in that of B. neustria $ and B. franconica ? 

 they are presumably large. 



In three more crossings the offspring consisted of both 

 sexes in normal proportions ; the females, however, con- 

 tained at best but few eesfs, and these abnormal in structure. 

 The crossings were of Smerinthus populi L. S and S. 

 ocellatus L. ? ; Saturnia pavonia L. $ and 6". pyri Schiff ? ; 

 S. pavonia L. $ and S. spini Schiff ? . 



Finally, in two more the sex-distribution appears again 



