Mr. J. O. Westwood's Description, S^c. 203 



XXX. — Description of a Case of Monstrosity occurring in 

 a Specimen of Dyticus marginalis, in which a portion of 

 the external marks of Sexual Distinction are abortive. 

 By J. O. Westwood, F.L.S. 



[Read 2nd July, 1838.] 



It has been remarked that the careful examination of animals in 

 a monstrous state of development, whether of excess or default, 

 is more serviceable in teaching the true nature of animal organ- 

 ization than the investigation of individuals in the normal state. 

 The case of monstrosity now under consideration appears to con- 

 firm, in some degree amongst the invertebrata, a theory hitherto 

 founded upon circumstances observed only in the vertebrata. 

 The insect in question is an individual belonging to the species 

 Dyticus marginalis, and, judging from the majority of its external 

 characters, is evidently a male insect. It was captured by the 

 Rev. F. W. Hope, in whose collection it is preserved, and to whom 

 I am indebted for an opportunity of examining it. 



The external marks of distinction of the male Dytici consist in 

 the dilated structure of the four anterior tarsi, the anterior pair 

 of which are moreover furnished with two large and many minute 

 cup-like organs on the under side or sole of the foot, which latter 

 occur also on the sole of the basal joints of the middle feet ; and in 

 the svTiooth and polished surface of the thorax and elytra, the latter 

 of which exhibit also three longitudinal rows of very minute im- 

 pressed dots. The females have the four anterior tarsi simple 

 and unfurnished, vvith larger or smaller cups, the sides of the 

 soles being provided with short strong spines ; the surface of the 

 thorax is covered with small impressions, and each of the elytra 

 is deeply impressed with ten deep longitudinal furrows, the surface 

 of the elytra being also generally covered with minute punctures, 

 and moreover exhibiting the three rows of larger dots also noticed 

 in the male elytra. 



In addition to the sexual distinctive characters mentioned above, 

 there are various others exhibited by the feet of a less important 

 character, which it will be serviceable to notice, especially as I find 

 no completely correct description of them by preceding authors. 

 Mr. Curtis being silent respecting them in his work illustrating 

 the characters of the British genera, and Dr. Erichson (whose 

 otherwise excellent Dissertation, entitled " Genera Dyticeorum," 



