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these we usually find extremely limited in the number of species ; for 

 being but a transitory passage from o^ie group to another, we may as- 

 sume that in the route she has not had leisure to look around her, and 

 create connate creatures, but has hurried on, to speak metaphorically, 

 until, having again settled in a new domicile, we find radiating fi'om 

 this centre, and variously ramifying from the several branches, a host 

 of allied forms, all participating in some predominant characteristic 

 with the radical type. At first the progress is gradual, but having 

 reached the extreme verge of the quitted group, and proximate to the 

 renewed'transformation the throes are convulsive, and the structure be- 

 comes most eccentric, exhibiting fi^equently affinities to several points. 

 The present group admirably illustrates these opinions. Thus in the 

 transition from the Tenthredinidse to the Ichneumonidae, we find the 

 progress at first gradual, by means of the remarkable genus Xyela, 

 if this be its true place, although it has, in so many respects, an inti- 

 mate affinity with the former family, yet fewer with the subsequent 

 Cephus; and here the first jump is made to Sirex, which by means of 

 Xyphidria is connected with Oryssus, but from each of these steps 

 however there is a leap. Having arrived at the limit of the group in 

 Oryssus, the contortion is very violent, for in this eccentric genus, 

 with all its anomalies of structure in the antennae and anterior tarsi of 

 the female, differing from everything else and peculiar to itself, we 

 find conjunctively a triple series of affinities, namely, one in a diver- 

 gent course by means of its ovipositor to Cynips, and two in a regular 

 line, forming the connection, through Megalyra, between the Tenthre- 

 dinidae and Ichneumonidae : and that this, in a family by itself, is the 

 true position of the genus Megalyra, the following brief summary of 

 connecting resemblances will sufficiently show. In the first place, the 

 neuration of the superior wings in Oryssus and Megalyra is very near- 

 ly identical ; in the next place, in both genera we find a channel for 

 the reception of the scape of the antennae running obliquely down- 

 wards from their insertion, past the base of the mandibles, and which 

 occurs nowhere proximately on the Ichneumon side of affinities ; the 

 specific character of a fascia across the superior wings, is also subsi- 

 diary to their corroboration : and then, the greatest transition having 

 to be made fi'om a cylindrical sessile abdomen to a petiolated one, 

 wdiat could we find so aptly executing this as in Megalyra, where we 

 observe an elongated metathorax embracing the base of the abdomen, 

 which is also cylindrical, a form nowhere found amongst the normal 

 Ichneumons, and the ventral plates likewise are of a firmer consis- 

 tence than in these, thus resembling those of the cognate Aulacidac, 



