No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 117 



iculum a constriction is formed which converts the proximal 

 portion into a thin cord but leaves the distal end expanded as 

 a hollow sac, which I shall call the terminal ampulla. The 

 remainder of the deferent duct — viz. the portion extending from 

 the sexual gland in the sixth to the anterior end of the tenth 

 segment is formed by a cord-like thickening in the splanchnic 

 wall of the three intervening somites. Anteriorly the cells 

 of the duct pass into the epithelium enveloping the germ-cells. 

 There is no lumen in the duct proper except towards its end 

 where it widens into the terminal ampulla. Thus only the ap- 

 pendage diverticula of the tenth segment go to form the ends 

 of the ducts ; in all the other abdominal segments the diverti- 

 cula break down and disappear, together with their respective 

 appendages, before the embryo reaches Stage H. In the 

 thoracic, oral and antennary segments, however, the diverti- 

 cula are converted into the muscles of the persistent ap- 

 pendages. 



The further history of the male ducts is readily followed in 

 partially stained embryos mounted in toto. Sex is determined, 

 so far as I have been able to make out, during or soon after 

 katatrepsis, at which time the appendages of the second to 

 the seventh abdominal segments disappear. Fig. 42 represents 

 the caudal end of an embryo just after katatrepsis (Stage J). 

 Appendages still persist on the eighth to eleventh segments 

 while the pleuropodia, not seen in the figure, have begun to 

 degenerate. The testes {ts^ and the spermaducts {in. d.) are 

 represented in blue. The former have shortened considerably 

 and moved caudad so that they now lie in the sixth and seventh 

 segments. The long terminal threads run forwards from the 

 anterior ends of the testes, while the spermaducts run back- 

 wards and end in the terminal ampullae {ta. in.) which still fit 

 into the cavities of the tenth pair of abdominal appendages 

 {ap. ^°). A section through these appendages is seen in Fig. 

 57, showing very clearly the connection of the ampullae (ta. m.) 

 with the ducts {in. d.). In front of this section the ducts have 

 no distinct lumen. 



In Fig. 43, taken from a slightly older embryo, the append- 

 ages of the eighth segment have completely disappeared, 



