OVA OP PENTHALEUS CAFIDARIUS, 



o7 



dition; and having exhausted the pabulum afforded by the albumen for its 

 growth and nourishment '^within," it is necessary that fresh materials be 

 obtained from ^'without:" this can only be effected by a twofold change, 

 which takes place as follows: — First, we have the shell membrane giving way 

 fjr the escape of the Yolk Sac, with its included germe. This does not 



always take place exactly in the same manner; 

 for sometimes the escape is made by the cupola 

 being thrust on one side, and the shell mem- 

 brane is broken up in various directions. (Figs. 

 G and 7.) While at other times the Sac forces 

 up the cupola by a pressure equally applied, 

 and causes it to fall off, after the manner of 

 the extinguisher-like calyx of Eschscholtzia. (Fig. 8.) 



The Second change consists in the breaking up of the Vitelline membrane, or 

 Yolk Sac, and of the consequent escape of the adult 

 embryo or larva. This takes place at any part 

 of the circumference of the membrane, except at 

 that portion which was situated under the cupola. 

 The reason of this seems to be owing to the 

 deposition of a white material, precisely similar 

 to that which covers the external membrane, and 

 which is analogous in function to the calcarious 

 shell in the case of birds; but as to its compo- 

 sition, nothing definite can be advanced.* For 

 what purpose the secondary shell exists: why it should occupy such a limited 

 portion of the Yolk bag, and in what way it is here secreted, are queries, 

 for the solution of which we will hazard no conjecture. The existence of 

 grooves on its surface, corresponding to those of the cupola, are also quite 

 discernible on the secondary shell. (Figs. 7, 8, and 9.) 



The Sac having ruptured, the larva, which is of a 

 bright crimson colour, escapes in the usual manner. 

 (See Figs. 9. and 10.) It presents a pair of distinct 

 eyes, but no feet, while the annular divisions of the body 

 are barely apparent. As to the process of development 

 in Ovo I can add nothing new, but will conclude with 

 a short extract taken from the last Edition of Dr. Carpenter's valuable work 

 on the ^^Principles of Physiology." (Page 387: — ) 



'*In all cases the embryonic mass within the egg is first converted into a 

 footless worm, resembling the higher Entozoa, or the inferior Annelida in its 



* Since wi-iting the above, I have been informed by Mr. Drummond, one of the members of the 

 Society, who has lately made some chemical investigations on tliis subject, that the homy-Kke 

 material, forming the shell of the Ovum, consists of Chitiiic; the foi'uiula of which is closely 

 allied to that of the Proteine compounds. It is well known that this substance enters largely 

 into the composition of the tegumentary system of Insects generally, and is especially abundant 

 in the Coleoptera. 



VOL. II. I 



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