Dear Sir,

In fulfilment of my promise, I write a few lines to inform you that the result of my observations on the young of the varieties of Theridion lineatum on quitting the cocoons that I had collected for the purpose of ascertaining whether on that occasion and for some time afterwards they would present any characteristics by which they might be distinguished from each other or not, completely confirms my opinion previously expressed, that no such characteristics can be perceived; and this remark applies also, as might be expected, to the young spiders in their customary haunts.¹ It would be well to extend the observations through the several stages of growth in the young of these varieties, but the undertaking is surrounded by so many and great difficulties as to render it scarcely practicable.

The colours on the abdomen of Epëira diadema² present considerable variety in adult specimens, but the design formed by their distribution is pretty constant; the young, however, on quitting the cocoon differ decidedly from the parents and cannot be distinguished from each other.

An additional motive for bestowing my tediousness upon you has been induced by meeting with a passage in Westring’s “Araneæ Svecicæ” having relation to the stridulous sound produced by several species of Theridia.³ At the conclusion of the description of Theridion serratipes,⁴ p. 175, he adds the following “Obs. Maris abdomen circa nervum, quo thoraci affixum est, valvula denticulata munitum, cujus usum sæpe animo perpendi, et tandem mihi fortuito contigit comperire hanc valvulam instrumentum stridoris esse, et quod thoracis basi, sub oculo armato transverse subtilissime rugulosa, ab animalculo applicatum, stridorem fere ut in Cerambycinis, Reduvio personato et multis aliis insectis reddebat. Hunc sonum audiebam, cum aranea, acu affixa, pulvillo acuum vel segmento papyri usque ad pectus apprimebatur, et tunc aranea, aut sua sponte, aut digitis erga anum attacta, abdomen sursum deorsum movebat, hujusque basin vel valvulam serratam erga basin thoracis affricabat. Femina organis iis caret. Idem post tempus plures mares Theridiorum stridentes mihi obvenerunt.”⁵

I may remark also that M. Westring terminates his description of the male of Theridion castaneum,⁶ p. 184, with this statement. “Instrumenta stridentia in basi abdominis et thoracis ut in Th. serratipede, 4-punctato, hamato, guttato et albomaculato adsunt.”⁷

Hoping that the above particulars may interest you, | I am, dear Sir, | very truly yours | John Blackwall.