-^^^ ^Nr. ^'■^ 



JOURNAL OF VARIATION. 



No 2. Vol. II. May 15th, 1891. 



THE GENUS ACRONYCTA AND ITS ALLIES. 



By Dr. T. A. CHAPMAN, F.E.S. 

 {Continued from page 2.) 

 CRONYCTA {Cuspidid) tridens. — We begin here that 

 section of the genus in which the eggs are laid 

 solitarily, the moth in the wild state probably taking 

 a flight after the deposition of each ^gg. The ^gg 

 (PI. VIII., fig. 2) of tridens is nearly colourless, almost glassy 

 when first laid, but acquiring a certain whitish opalescence as 

 the young larva within is developed. Its greater size, and, to a 

 slight degree, the ribbing, render it only slightly less favourable 

 for the observation of the embryonic development than those 

 of Botys hyalinalis, for the opportunity of observing which 

 species I am indebted to Mr. Jeffrey, of Ashford. The &gg 

 being solitary takes the very regular form of a portion of a 

 sphere, less than a hemisphere, or roughly, that of a bun. The 

 diameter is '83 mm., and height '38 mm. The ribs are 38 in 

 number ; in all the Acronyctas this number varies, and the 

 numbers I give are either the average or the actual number of 

 a particular specimen counted. The Q.gg of tridens rarely, if 

 ever, exceeds 44 ribs, that oi psi as rarely has less than 45. 

 In colour, or rather want of colour, secondary ribbing, form, 

 etc., they seem to be identical. When about to hatch, the 

 young larva is very conspicuous inside, the head forming a 

 central black spot. 



The newly hatched larva (PI. VI., fig. 2) is paler than it 

 shortly becomes, but the head is already black, and the pale 

 and dark segments are clearly pronounced. Each tubercle is 

 a large flat plate, somewhat angulated, so as to fit against 

 and amongst the others ; this feature is common to a number of 

 Acronyctas. The trapezoidals are thus somewhat pear-shaped, 

 the anterior with the narrow end backwards, the posterior with 



