REPRODUCTIVE SYSTEM. 59 



described, to a fold of skin, on each side of the sack : these 

 two folds, I have called the ovigenous frcena (PI. IV, fig. 2/). 

 M. Martin St. Ange, describes an orifice under the 

 carina, by which he supposes the ova to enter the sack ; 

 this, after repeated and most careful examinations, I ven- 

 ture to affirm does not exist; on the contrary, I have 

 every reason to believe that the ova enter the sack in the 

 following curious manner. Immediately before one of 

 the periods of exuviation, the ova burst forth from the 

 the ovarian tubes in the peduncle and round the sack, 

 and, carried along the open circulatory channels, are col- 

 lected (by means unknown to me) beneath the chitine- 

 tunic of the sack, in the corium, which is at this period 

 remarkably spongy and full of cavities. The corium 

 then forms or rather (as I believe) resolves itself into the 

 very delicate membrane separately enveloping each ovum, 

 and uniting them together into two lamellae ; the corium 

 having thus far retreated, then forms under the lamellae 

 the chitine-tunic of the sack, which will of course be of 

 larger size than the last-formed one, now immediately to 

 be moulted with the other integuments of the body. As 

 soon as this exuviation is effected, the tender ova, united 

 into two lamellae, and adhering, as yet, to the bottom 

 of the sack, are exposed : as the membranes harden, the 

 lamellae become detached from the bottom of the sack, and 

 are attached to the ovigerous fraena. To demonstrate this 

 view, an individual should have been found, with both the 

 old and new chitine tunic of the sack, and with the lamellae 

 lying between them ; this, I believe, I have seen, but it 

 was before I understood the full importance of the fact : 

 a great number of specimens would have to be examined 

 in order to succeed again, for the changes connected with 

 exuviation supervene very quickly. I have, however, 

 several times found the ova so loose under the sack, as 

 to be detached with a touch from the ovarian tubes ; 

 and I have twice carefully examined specimens, which 

 had just moulted, as shown by even the mandibles being 

 flexible, in which the lamellae had not become united to 



