68 REPORT— 1842. 



only to distinguish adult males from females, but likewise from immature individuals 

 of both sexes. This knowledge is useful in preventing him from falling into the too 

 common error of mistaking young spiders for old ones, and of describing them, and 

 the sexes of spiders of the same kind, as distinct species. 



When any doubts exist respecting the specific identity of spiders of different 

 sexes, which have been regarded as belonging to the same species, they frequently may 

 be set at rest by placing the spiders together in captivity and noticing whether they 

 pair or not. 



The great diversity of structure observable in the palpi and palpal organs of male 

 spiders supplies excellent specific characters, and indeed frequently presents the 

 only available means of distinguishing species of similar colours and dimensions from 

 each other; but when we consider that this diversity of structure extends to spiders 

 connected by the closest relations of affinity, it is perhaps in vain to expect that it will 

 ever be applied with much success to the establishment of genera. 



Account of a Species of Ichneumon, whose Larva is jxirasitic on Spiders. 

 By John Blackwall, F.L.S. 



Immature spiders of the species Epe'ira autriada and Epe'ira cucurbltina, and adults 

 of the species Linyphia minuta and Linyphia pusilla, are frequently infested by the 

 larva of a small Ichneumon, which feeds upon their juices and ultimately occasions their 

 de;\th. This parasite is always attached to the upper part of the abdomen, near its 

 union with the cephalothorax, generally in a transverse but occasionally in a longi- 

 tudinal direction, and, though it proves a source of constant irritation, is secured by 

 its position from every attempt of the spider to displace it. Being apodous, it ap- 

 pears to retain its hold upon its victim solely by the instrumentality of the mouth 

 and of a viscid secretion emitted from its caudal extremity. More than one larva is 

 never seen on the same spider, which, indeed, could not supply sufficient nourish,- 

 ment for two. 



In the earlier stages of its growth this parasite has an oblong oviform figure, 

 somewhat depressed on the under side ; it is whitish with a faint tinge of yellow ex- 

 tending along the medial line, which seems to be occasioned by the contents of the 

 viscera. At this period of its existence the external covering presents a smooth 

 uniform surface ; but when it has completed its moultings and attained its full size, 

 the head becomes visible, the body exhibits thirteen distinct segments, and the pre- 

 vailing hue is pale greenish yellow. 



When about to assume the pupa state, it kills the spider which has supplied it 

 with sustenance by rapidly exhausting its physical energies, and quitting it con- 

 structs on some adjacent object a cocoon of a quadrilateral figure tapering to its ex- 

 tremities, which is composed of pale yellowish white silk of a compact texture. 

 After the lapse of a month nearly, the perfect Ichneumon issues from the cocoon, and 

 prepares to carry on the work of destruction assigned to its species ; a preliminary 

 step towards which is the deposition of her eggs by the female on the bodies of her 

 victims, care being taken that one only is attached to the same spider. 



It is a fact deserving of notice, that immature spiders infested with the larva of 

 this Ichneumon do not change their skins. Were it not for this admimble provision 

 of Providence, the larva, cast off with the integuments in the act of moulting, would 

 inevitably perish, and the important purpose which its remarkable economy is so evi- 

 dently intended to subserve, namely, the keeping of these deadly enemies of the in- 

 sect tribes within due limits, would fail to be accomplished. 



The author described minutely the characters of the female and male Ichneumon, 

 which he conjectures may be unknown to entomologists. 



Mr. Turner exhibited specimens of Goliathus regius and Goliuthus giganteus. 



Dr. Lankester drew attention to a microscopic animal that had been found the 

 day previous in the Botanic Garden, covering the stems of the Chara flexilis, and 

 giving them a loose gelatinous white appearance. The moment they were touched 

 this character disappeared, from some contractile power possessed by the animal. 



