MORPHOLOGY OF THE LEPLDOPTERA. 163 



fig. 47). In cross sections the hypodermis is marked by vertical lines indicating- 

 elongate cells ; the nuclei are small and stain very darkly (PI. XVII. figs. 18, 19). A 

 detailed figure of a section through the walls of the azygos oviduct beneath the anterior 

 vesicle is given (PL XIX. fig. 61), from which it will be seen that the walls of the 

 oviduct, like the walls of the vesicle, have the same histological appearance as the cells 

 of the hypodermis from the body-wall. In this figure there is also shown a coating or 

 envelope of tissue (m) exterior to the layer of hypodermic cells. Similar tissue is found 

 investing more or less the bursa copulatrix, receptaculum seminis, median and posterior 

 portions of the azygos oviduct. It has, under a low power of the microscope, a finely 

 granular look, quite different from that of the fat-body. Under a high power it appears 

 to consist of minute irregularly shaped cells. It is present in later stages, and is found 

 to assume, when a specimen is stained with borax carmine, a pink colour, quite distinct 

 from the more yellow colour of the fat-body. It seems to me, in fact, composed of 

 mesoblast cells derived from the cceloniic fluid (?), which give origin finally to the 

 muscular and connective tissue coats of the genital apparatus, the invaginated hypo- 

 dermis forming only the epithelium. 



(3) Growth and Changes with the Bursa. Copulatrix in direct 

 union with the azygos oviduct. 



The period covered by this stage lasted in my specimens for about four days. The 

 changes in shape and size which take place in the parts already formed will be readily 

 understood from a study of PI. XVII. figs. 38-15 and the following brief description. 



The bursa copulatrix is at first a pyriform vesicle, with no stalk at all worth men- 

 tioning. It lies in the middle line and is placed very nearly vertically, a position which 

 is exchanged for one slightly tilted backwards, then for one turning forwards and 

 inclined more or less to the animal's right side, and last of all for one pointing straight 

 forwards on the left side of the animal. The stalk or duct of the vesicle grows con- 

 siderably in length, and becomes well marked off from the vesicle itself. The latter 

 commences to grow somewhat later, and the sharp distinction between it and its stalk 

 at the place where the two parts unite, may, as in the specimen figured PL XVII. fig. 11, 

 be lost to a certain degree. This, however, is not invariably the case. 



The receptaculum seminis is at the beginning of this period short and sharply bent 

 down upon itself to the left ; but it increases very rapidly in length, and the portion 

 bent down becomes straightened. The whole structure is, in the early part of this stage, 

 strongly inclined backwards, and to the animal's left side, but becomes by degrees more and 

 more vertical. Its base or point of origin is at first placed a little to the left, and slightly 

 behind the base of the stalk of the bursa copulatrix. The two gradually separate, and 

 towards the end of this stage, the point of origin of the receptaculum is very decidedly 

 behind the origin of the stalk of the bursa and on the median dorsal aspect of the azygos 

 oviduct. 



The changes undergone by the region of the posterior vesicles which gives origin to 

 the paired sebaceous glands of the imago are considerable. At the beginning of the 



