678 THE GENERATIVE ORGANS. 



genital spine. The receptacula and their ducts are lined by a 

 cuticular intima. This membrane is of a dark-brown colour in 

 the capsules, and exhibits transverse rings like those of a 

 tracheal vessel. The intima of the duct is colourless, and 

 exhibits only faint rings. 



The duct is a thick-walled tube with walls of from 20 ^ to 

 25 /A in thickness. In the young imago, externally to the 

 intima, both the capsule and duct have an epithelial and peri- 

 toneal layer, and are closely surrounded by fat-cells. In the 

 adult insect the epithelial layer is no longer demonstrable, but 

 both capsule and duct are covered by a layer of highly-developed 

 striated muscle-fibres. In the impregnated female, the capsules 

 are filled with closely-coiled spermatic filaments. 



3. ON THE STRUCTURE OF THE EGG IN THE BLOW-FLY. 



The Egg. The mature egg of the Blow-fly measures 1*42 to 

 i'49 mm. in length, and has the form of an elongated ellipsoid, 

 which is smaller at its anterior and broader at its posterior end. 

 Its long axis is slightly curved, so that its ventral surface is 

 convex and its dorsal surface is flat, or even slightly concave. 

 It exhibits a micropyle at its anterior end, from which a canal, 

 or rather groove, extends to very near the posterior pole of 

 the egg, along its dorsal aspect. 



In the ovaries and oviducts the anterior extremities of the 

 eggs are directed forward, and in the uterus the dorsal aspect of 

 the egg is towards the dorsum of the insect. The embryo is 



Bibliography : 

 335. MEISSNER, G., ' Beobachtungen iiber das Eindringen der Samen- 



elemente in den Dotter.' Zeitsch. f. w. Zool., Bd. vi., 1855. 

 336 LEUCKART, R., ' Ueber die Micropyle und den feineren Bau der 



Sclialenhaut bei den Insecteneiern.' Archiv. f. Anat. und Physiol., 



1855. 



337. KoksriiKLT, E., 'Zur Bildung der Eihiillcn, der Micropylen und 

 Chorionanhange bei den Insecten.' Nova Acta C. L. C. Acad., 

 Bd. li., 1887. 



338. C'HOLODOSKY, N., ' Ueber einige Formen des Blastopors bei mero- 

 blastischen Eiern.' Zool. Anzcig. Jahrg. xiv., p. 159, 1891. 



