Miscellaneous . 171 



garded as a diffused vitellogene, analogous to that indicated in other 

 Cotylide worms. 



The Pontobdella envelopes its ovum in a cocoon fixed hy a pedicle 

 to submarine bodies ; this is figured by Hesse and Van Beneden, but 

 from an altered specimen, unless it belongs to a different species. 

 The animal embraces the cocoon with its anterior disk to complete 

 and fix it. Hence, and from the facts observed in other species, 

 the author concludes that the so-called salivary glands furnish the 

 material for this protective envelope of the ova. — Comptes Rendus, 

 July 13, 1868, pp. 77-79. 



Considerations upon the fixation of the limits between the Spedea and 

 the Variety, founded upon the study of the European and Me^nter- 

 ranean species of the Hymenopterous Genus Polistes (Latr.). By 



M. SlCHEL. 



I. For several years the question of the mutability or immutability 

 of the species has been afresh brought under discussion, and vividly 

 attracts the attention of zoologists. Nothing can contribute more 

 to exhaust this question and to pave the way to its solution, by aiding 

 powerfully to fix the limits between the species and the variety, than 

 the profound study and exact statistics of certain genera of insects 

 richly represented in individuals, and possessing a sufficient number 

 of species common in our climates to allow us to study them on a 

 large scale in regular and complete series. Series captured in the 

 nests especially, by permitting the comparison of allied species and 

 the exact observation of the transitions between each species and its 

 varieties, will singularly facilitate our conclusions, and give them a 

 high degree of certainty. 



Such a genus is the Hymenopterous genus Polistes, represented in 

 the whole of Europe, in Algeria, and in the western part of Asia by 

 four species (three of which are very common even in the environs of 

 Paris), viz. P. gallicus, higlumis, diadema, and Geoffroyi. 



II. But these last three species are identical with P. gallicus, and 

 only differ from it as varieties. It is this opinion that I endeavour 

 to establish here by numerous and, I think, convincing proofs, in 

 order to show for once how the study of the Hymenoptera on a large 

 scale and on the living animal may contribute to fix the limits be- 

 tween the species and the variety. 



III. The above four species may be well characterized ; but their 

 diagnostic characters are neither constant nor essential, as is proved 

 by the following propositions, deduced from long-continued and accu- 

 rate observations : — 



1 . The subvarieties are so numerous that we may at pleasure create 

 new varieties among them. 



2. The transitions between the different varieties are so frequent 

 and so insensible that it is often impossible to say where one variety 

 or subvariety ends, and where the next one commences. 



3. In the same nest we see hatched simultaneously or sucodssirely 



