No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 119 



have long since disappeared and the pleuropodia have lost 

 their organic connection with the embryo, so that only two 

 pairs of abdominal appendages persist, the stylets {st. \ap 9] ) 

 and the cerci (cc. [^?/"]), both provided with setae. The 

 pointed fusiform cerci are now folded back so as to bring 

 their insertions on the anal segment into view. 



Beyond this stage the development of the male ducts was 

 not followed in XipJiidiinn ensifcrmn, but several larval stages 

 of an allied species, X. fasciatum, were studied for the purpose 

 of connecting the embryonic with the adult condition. 



It will be noticed that in Xiphidi-iLvi cnsifefiim there exists 

 at the time of hatching no external opening to the sperma- 

 ducts; the ampullae are completely closed sacs applied to 

 the ventral hypodermis of the ninth abdominal segment, and 

 the ducts connecting them with the testes have no lumen. 

 In the X. fasciatum larva 10 mm. long the ejaculatory duct 

 has made its appearance as an unpaired invagination of the 

 hypodermis in the median line between the ninth and tenth 

 segments. Fig. 47 shows the sexual organs of such a larva 

 seen from within, the ventral scutes of the tenth and anal seg- 

 ments having been entirely removed. The prominent terminal 

 ampullae, which become the seminal vesicles of the adult, are 

 considerably enlarged and their walls have increased in thick- 

 ness. The short spermaducts, now provided with a small 

 lumen, run from the under surface of the sacs to the prom- 

 inent testes. Only the outer opening of the invagination 

 which is to form the ejaculatory duct is seen at m.o. It runs 

 forward as a flattened chitin-lined depression beneath the 

 seminal vesicles. Sagittal sections show that there is as yet 

 no communication between the lumina of the mesodermal and 

 ectodermal portions ; it is not till a later stage that such a 

 communication is established. 



3. The Female Ducts. 



The oviducts, like the vasa deferentia, are derived from a 

 pair of coelomic appendage-diverticula, but in the female the 

 diverticula belong to the seventh abdominal segment. The 

 diverticula of the female embryo also become constricted 



