174 PEOF. W. H. JACKSON ON THE 



partial homologue of the vaginal orifice in other orders of Insecta. It opens in the 

 sternum of the eighth somite, the typical position of the vaginal aperture, as disclosed 

 by the researches of de Lacaze-Duthiers. It is only a partial homologue for the 

 following reason. A little consideration shows that the true vaginal aperture is the 

 opening of the first into the second section of the azygos oviduct. The bursal aperture 

 is, strictly speaking, the ventral opening of the second section, and it leads into a tube 

 which has been secondarily developed by the ventral closure of a furrow. Its persistence 

 may be explained on the supposition that it is necessary for copulatoiy purposes, and 

 points rather to the conclusion that the bursa copulatrix and receptaculum seminis were 

 differentiated structures at a time when the second and third sections of the azygos 

 oviduct were still a continuous open furrow. The lateral position of the bursa and its 

 separation from the azygos oviduct are probably late features in the phylogenetic history 

 of the Lepidoptera, subsequent even to the closure of the furrow. 



The existence of a second or posterior aperture is probably to be attributed to the 

 advantage gained by a terminal position for the aperture through which the ova are 

 laid. The remarkable way in which this aperture shifts backwards seems to point very 

 distinctly to this explanation, especially as the Lepidoptera are entirely devoid of the 

 outgrowths which form the ovipositor in some orders, e. g. most Orthoptera. 



It may therefore be said that there are three stages traceable in the evolution of the 

 genital ducts in the Lepidoptera : an Ephemeridal stage, which ends towards the close 

 of larval life ; an Orthopteran stage, indicated during the quiesceut period preceding 

 pupation ; and a Lepidopteran stage, which begins with the commencement of pupal 

 life. As was mentioned before (p. 149) the female genital ducts of Nematois metalllcus 

 possess but a single external aperture, and the bursa opens into the dorsal wall of the 

 azygos oviduct. It is possible that a better acquaintance with the anatomy of the 

 Micro-Lepidoptera may disclose transitional or primitive states of the organs in question, 

 just as Walter's researches (Jenaische Zeitschrift, xviii. 1884) have clearly shown that a 

 primitive biting condition of the mouth-parts exists at the present day in some Micro- 

 Lepidoptera, and more particularly in the genus Ilicropteryx. 



There is one other point to which it is worth while drawing attention. What is the 

 significance of the cuticular secretion formed by the hypodermic cells at a certain period 

 of pupal life ? Is it analogous to what occurs in the higher Amphibia, lizards and 

 snakes, where certain cells break down completely and provide a liquid which facilitates 

 the process of casting the old cuticular epidermis ? If this be the explanation it would 

 naturally be a process occurring at every moult. Whether such is the case with the 

 moults of the caterpillar I do not know, but the surface of a newly-formed pupa is moist 

 with a liquid, and it is the hardening of this liquid when exposed to air that glues the 

 wings and legs to the surface of the body. Or is the secretion to be regarded as a 

 modified cuticle thrown off within the first formed pupal cuticle ? It is well known that 

 an Ephemeron casts a thin pellicle after it has escaped from the sub-imago state, and 

 there is some evidence to show that the same process occurs in the Lepidoptera. 

 Professor Westwood drew my attention some time ago to a passage in Curtis's ' British 

 Entomology,' in the description of plate 147, where that most accurate authority records 



