220 Observations on Piiupla pomoriim 



larvae. The labium {I) is ovoid in form and measures -14 mm. in length 

 and -10 mm. broad (Text-fig. 4). Its free margin is simple and undivided; 

 a pair of papillae {'p), similar in form and size to those found in the first 

 maxillae, are also present. These are similarly represented in the young 

 larvae by a pair of groups each comprising seven minute papilla-like 

 structures. From their position and constancy of occurrence, these struc- 

 tures suggest their possibly being the vestigial counterparts of the labial 

 and maxillary palpi, and have been regarded as palpi by Cushman in his 

 description of the larva of Thesolochus conotracheli (1916, p. 853 and Fig. 8). 

 The fact that in Pimjjla pomorum, at any rate, they are represented in the 

 young larvae by groups of minute papillae, militates against this inter- 

 pretation of their morphology. 



The trunk segments are separated by deep, well-defined intersegmental 

 grooves, and segments 4 to 10 have the tergal region raised in such a 

 manner as to form a row of transverse mid-dorsal tubercles or pseudo- 

 pods. These are only slightly developed and are more noticeable from a 

 lateral rather than from a dorsal view (Plate XII, fig. 2). In a similar way, 

 the lateral regions of the same segments are slightly produced outwards to 

 form rounded mamilla-like swellings. Ten pairs of spiracles are present, 

 and are situated on the first, second, and fourth to eleventh segments. 

 The first pair is placed on the posterior region of its segment, near the 

 intersegmental groove separating it from the succeeding segment. The 

 second pair of spiracles is vestigial and non-functional. These spiracles 

 are very small and hard to detect ; they occupy a position on their seg- 

 ment similar to that of the preceding pair. No spiracles are present on 

 the third segment, while the remaining eight pairs are situated far for- 

 wards on their respective segments. 



7. COMPARISON WITH LARVAE OF OTHER ICHNEUMONOIDEA. 



In the possession of a well-defined head and thirteen body segments 

 the larva of Pimpla pomorum conforms to the usual type found among 

 Ichneumonoid larvae. This same number of segments has been found to 

 obtain in a number of species, notably by Xambeu (1898)^ in Pimpla 

 oculatoria Grav., by Seurat (1899) in P. mexicana, by Giraud (1863) in 

 P. detrita Holmg. (gramdnellae Grav.), by Ratzeberg (1844) in Exochilium 

 (Anomahn) circumflexum L., by Riley (1888) in Thalessa lunafor Fab., 

 by Berthoumieu (1894) in Ichneumon ruhens Fons., by Morley (1903) in 



1 Xambeu mentions (p. 239) twelve segments in P. oculatoria, the hindmost being 

 "prolonge par un mamelon retractile"; the latter structure, however, appears to be the 

 reduced thirteenth segment. 



