M. Leuckart on the Reproduction of Bark- lice. 417 



loose in the oviduct ; it is rather only an annular thickening in 

 the delicate chitinous coat which lines the entire oviduct. 



In Chermes (figs. 1-3) there is the same chitinous bund as in 

 Phylloxera, and also an evident, though less distinctly separated, 

 funnel-shaped or pouch-like oil-vesicle ; but the gland is very 

 strikingly different. It appears on each side as a flattened ear- 

 like appendage of an oval form, with a space of a similar shape 

 in its interior, and a delicate, strongly granulated, chitinous 

 lining. The exterior surface of this chitinous wall is drawn into 

 numerous folds, which are continued between the neighbouring 

 cells of the gland, and are gradually lost. At the point of in- 

 sertion of the glands, the oviduct (fig. 2) forms an inflation of 

 considerable size but with little muscularity, which is constricted 

 in the middle by the elastic contraction of the chitinous band. 

 As soon as an egg passes this spot, this constriction is effaced, 

 whilst the chitinous band at the same time gradually expands 

 (rig. 3) and acquires a rather smooth appearance. I will not 

 here dwell further upon the mechanical importance of this ar- 

 rangement, hitherto discovered only in the Bark-lice; it is, 

 however, evident that in it the elasticity of the chitinous band 

 is of the highest importance. 



To the preceding account of the structure of the generative 

 organs in the Bark-lice, and their remarkable mode of reproduc- 

 tion, I shall take the liberty of adding a few further observa- 

 tions. 



The first relates to the occurrence of the two different forms 

 indicated by us amongst the parthenogenetic females of these 

 animals. 



We have characterized these two forms as wingless and winged. 

 It must not, however, on this account be supposed that their 

 distinctions are limited to the presence or absence of organs of 

 flight, and that the differences here occurring may be compared 

 to those which we meet with as regards the formation of the 

 wings in many species of Orthoptera (see Fischer, Entomol. 

 Zeitung, 1852, p. 15) and Hemiptera. The distinctions of these 

 two forms are far more considerable ; they extend to the entire 

 external organization of the individuals in question, to their size, 

 form, and the structure of the segments of the body, and affect 

 even the internal structure in a remarkable manner. Without 

 a knowledge of their genetic relations, the two forms would ne- 

 cessarily be regarded not merely as representatives of different 

 species, but even of different genera. The difference is scarcely 

 less than that in the sexes of the Coccina. In other words, it is 

 a complete dimorphism that we here meet with. 



That these distinctions are also expressed in the mode of life 

 is no more than might have been expected ; and indeed, on the 



Ann. & Mag. N. Hist. Ser. 3. Vol. iv. 27 



