OF GENERATION. 335 



the aorta, but without admitting of the passage of the one into the other. 

 What Joh. Miiller considers as a continuation of the aorta, or as a 

 blood-vessel, I conceive to be the inner coat or mucous tunic ; his egg- 

 tube tunic, on the contrary, as the exterior or muscular tunic. 

 Nevertheless, the filament may be hollow as far as the heart, without, 

 therefore, necessarily opening into the aorta. If such a passage existed, 

 and it were of physiological importance to the development of the egg 

 germs, it would be found in all female insects, but which, as Miiller 

 himself admits, is by no means the case. The contents of the hollow 

 connecting filament is a white granulated mass, which extends in it as 

 far as the heart, and can be even still detected where the filament has 

 already dilated into the egg tube. From this point the mass becomes 

 more and more consolidated together, and now assumes the appearance 

 of a thick lump, which is found between every two egg germs. We 

 first find the egg germs in the superior distended portion of the egg- 

 tube, and indeed in their peculiar oval form, whereas the mass between 

 two eggs is much smaller in compass, the egg-tube consequently between 

 every two egg germs is somewhat contracted. The egg germs, how- 

 ever, increase in size the lower they are placed in the egg tube, so that 

 the lowest is the largest of all, and the highest is the smallest. This 

 highest egg germ is almost of the same size as the mass placed between 

 it and the second one, which mass Miiller calls the placentula, and the 

 first egg germ also appears to have gradually formed itself from the 

 white granulated substance lying above it. 



The development of the last egg germ, lying at the base of the egg- 

 tube, takes place thus : the placentula beneath it, in consequence of 

 impregnation, enlarges, and gradually re-models itself until it takes the 

 form of a cone, the apex of which is turned towards the egg germ. 

 Its base, or broad basal surface, therefore, separates the internal mem- 

 brane of the egg-tube until it comes into direct contact with the 

 exterior or muscular tunic, and becomes organically connected with it by 

 means of tracheae, whereby a dark annular girdle is formed at the base 

 of the egg tube, which Joh. Miiller calls the ring of the vessel. 



Hitherto the egg germ has no pellicle, or shell, but it consists of a 

 thick, uniform, gelatinous mass. Now, after the placentula has dis- 

 tended itself, it is probable that the impregnation of the egg germ 

 proceeds from it ; and when this has taken place the shell commences 

 to be formed from above downwards, so that it, as it were, grows over 

 it, commencing at its upper end. Contemporaneously with it is the 



