No. 1.] CONTRIBUTION TO INSECT EMBRYOLOGY. 1 33 



obscure, for why should the ampullae in Xiphidiuni move from 

 the tenth into the ninth segment ? The answer to this enigma 

 depends on further comparative embryological research. The 

 long persisting closure of the ostia of the male ducts in Ephe- 

 merids is probably an embryonic trait. That the vagina and 

 ejaculatory duct of higher insects, may have arisen from a 

 simple intersegmental depression like the ovivalvula receives 

 some support from the fact that the ectodermal portions of the 

 sexual apparatus make their appearance so late ontogenetically. 

 To obtain in XipJiidiimi a condition essentially like that in 

 Ephemerids it would only be necessary to have each terminal 

 ampulla in both sexes open to the exterior. 



The original termination of the sexual ducts in modified 

 ambulatory appendages — which is so clearly seen in both 

 sexes in embryonic Orthoptera — is very probably a primitive 

 feature. In the Malacostraca among Crustacea and in Dip- 

 lopod Myriopoda the sexual ducts terminate on more or less 

 modified ambulatory limbs ; in both sexes in the former group, 

 only in the males in the latter. In the insect embryo the 

 male genital appendages are larger than those of the female; 

 hence, perhaps the larger size of the ampullae filling their 

 cavities. The ampullae are probably very important structures 

 from a phylogenetic standpoint. They may perhaps represent 

 the nephridial Endblasen of Pcripahis and Annelids, providing 

 these latter structures are mesodermal. In Annelids the End- 

 blasen occasionally function as temporary receptacles for the 

 sexual products, a function which seems to have been retained 

 in the male insect, where they become the vesiculae seminales. 



Within the group Eutracheata^ the position of the sexual 

 openings is subject to great variation. Thus in Diplopods and 

 Pauropods the ducts open behind the second pair of legs, 

 usually between the second and third segments. In Chilo- 

 poda, on the other hand, they open on the penultimate seg- 

 ment. In the Symphyla the unpaired genital orifice is situated 

 on the fourth segment, which probably corresponds to the first 

 abdominal segment in insects. Even within the division 

 Apterygota great variation is observable. In the Collembola in 



1 Under this heading I would include the Myriopoda and Hexapoda. 



