Miscellaneous. ETE 
garded as a diffused vitellogene, analogous to that indicated in other 
Cotylide worms. 
The Pontobdella envelopes its ovum in a cocoon fixed by 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 Species and 
the Variety, founded upon the study of the European and Mee iter- 
ranean species of the Hymenopterous Genus Polistes (Latr.). By 
M. SIcHeEt. 
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, biglumis, 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. 
Ill. 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 successively 
