OVA OP PENTIIALKOS CAPIDARIUS. 



and recognise their nature. Their diminutive size is a character common to 

 most species of the same family, (Acaridce.) To obtain, however, a more 

 satisfactory knowledge of their morphology and construction, it is necessary 

 to subject them to much higher magnifying powers, and the drawings now 

 before the Society, represent them at different stages of development, magnified 

 two hundred and fifty diameters linear. 



The chief points of interest, to which we may direct our attention, bear 

 reference to their external configuration; the changes in form during develop- 

 ment; and the manner in which the mature embryo or larva makes its 

 escape from the outer covering or shell. 



The general form then may be at once recognised as that of a sphere 

 flattened and depressed from above. (See Figs. 2 

 and 3.) This button-like character is by no means 

 an unfrequent appearance in the eggs of insects 

 generally; and though I have not seen any pre 

 cisely similar illustrations to those before us in the 

 works of recent entomological writers; there is, 

 nev^ertheless, figured in the great work of Swammerdam, Plate xxxiii. Fig. 1, 

 a very similar form of an egg, belonging to one of the Noctuae, or Post 

 Meridian Moths; it is devoid, however, of certain markings, which, in the 

 specimens before us, have a very chaste appearance, and which represent a 

 series of alternate elevations and d.epressions, (twenty-five in number,) running 

 from a central elevated point, to the outer border of the button-like surface. 



When viewed laterally, and especially if the specimen be immersed in some 

 transparent medium, not only are these morphological features readily con- 

 firmed, but we observe, through the outer covering, or shell- 

 memhram, a small round opake boJy, situated immediately _ 



under the central prominence, as seen as Pig. 4-. This, there 

 can be little doubt, corresponds to the Yolk, or Vitellus in 

 the Ova of birds and other animals, being enclosed in a special 

 and distinct envelope of its own, constituting the Yolk Sac, 

 or Vitelline membrane. 



Keeping our attention fixed from time to time on the same Ova, we observe 

 that this opake body or Yolk increases at the expence of the surrounding 

 medium, or albumen, which is situated between it and the shell membrane, the 

 alterations in form of which latter structure, are almost entirely confined to 

 the cupola, or cup-shaped surface. I have employed the term Cupola here 

 as expressive of the change which this part of the covering 5 



undergoes, becoming, as it does, in course of development, 

 dome-shaped, or convex; (see Fig. 5,) whereas in the first 

 instance we found it depressed or concave; its central point 

 only being excepted. (Fig. 3.) 



We have now arrived at the period when the embryo, or 

 germe, enclosed within the Yolk Sac, has nearly attained its mature con- 



