300 BRITISH LEPIDOPTERA. 



eggs, whilst the latter, as yet, have never shown themselves capable of 

 development, except in the case of S. hybr. schaufussi, yet the males 

 of the hybrids will readily pair with, and easily fertilise, the females 

 of either parent stock. The experiments further brought out many 

 incidental points ; among others, they show that the male S. pavonia had 

 very little influence on the progeny of a $ ,S. spini, with which it paired, 

 whereas a male S. pavonia influenced greatly the progeny of a $ 

 S. pyri. Comparison of certain characters, exhibited by the larvae 

 and pupae of the three species — spini, pavonia and pyri — always 

 resulted in placing spini in the lowest position genealogically, and 

 pyri in the highest, so that pylogenetically the species always arranged 

 themselves — spini, pavonia, pyri — spini being the oldest form. In the 

 crossings, the oldest species, spini, was able to cling to its characters 

 more strongly than the younger pavonia, and this latter again more 

 strongly than the still younger pyri. Standfuss further notes that 

 in the reciprocal crosses between S. pavonia and S. spini, the male 

 element had more influence on the resulting form of the hybrid 

 than the female. He further states that the experimental test of 

 the reproductive capabilities of male hybrids, when crossed back 

 with females of both parent forms, showed that the fertility of these 

 primary hybrids was greater when paired with the phylogenetically 

 older form than with the phylogenetically younger, so that the 

 physiological characters of the primary hybrid were nearer to the 

 phylogenetically older form than the younger." The chief points re- 

 lating to the development of these hybrids are formulated (E71L, 

 xxxiii., pp. 346 — 347) as follows : 



1. The secondary hybrids were not only produced by pairing primary male 

 hybrids with females of the parent species, but also with the females of a third 

 species. 



2. A larger percentage of the broods of crossings of these primary hybrids with 

 females of the phylogenetically oldest of its parents developed, than with the females 

 of the younger. 



3. The resulting brood shows in general the same characters as in the primary 

 hybrids, in biological and physiognomical respects, but with a larger individual 

 variability. A tendency was shown to follow the line of development of the 

 phylogenetically older form of the two, and in the three species the phylogenetically 

 oldest form. 



4. In a less degree there is to be found in some male individuals a capability 

 and inclination to individual development in new directions within a narrow limit. 



5. Besides males capable of limited and individually varying degrees of repro- 

 duction and females mostly sterile, or only fertile to a slight degree, there appeared 

 among certain secondary hybrids a relatively large number of gynandromorphous 

 specimens in various crosses and in varying proportions. 



6. The physiological affinity of the secondary hybrid males, and also of the 

 somewhat fertile females, to the related types, has not yet been ascertained, so that 

 nothing definite can be said about it. An increase of fertility, compared with that of 

 the male parent, could not be ascertained in any of the numerous cases investigated, 

 but, on the contrary, generally a decrease. 



7. The broods of secondary hybrids, whether from an inpairing of these forms 

 or from crossing with a true Saturnia ? has produced up to the present only males, 

 which were certainly capable of reproduction. 



Standfuss gives (Ha/idbucIi,^LC, pp. 100 — 107) some most interest- 

 ing suggestions as to the relative age of the three European species of 

 Saturnia, as suggested by the oval, larval, pupal and imaginal structure, 

 and details at length reasons for considering S. spini to be the oldest 

 form and S. pyri the most recent. The chief of these are as follows : 



1. The larva of S. spini maintains its original black colour throughout its life. 

 S. pavonia loses this, sometimes in the 3rd stage, always in the 4th or 5th. S, 



