36 Introduction to Animal jMorphology. 



organs like ovaria, but producing- gemmules (more or 

 less resembling true ova), which do not require any- 

 male stimulus for their development. These organs are 

 called pscudovaria, and the gemmules are viviparously 

 produced. Each of the deuterozooids can produce in 

 these cases tritozooids, &c., as long as suitable con- 

 ditions of temperature and food continue ; but on the 

 occurrence of some unknown checks upon this process, 

 the individuals of the last brood develop perfect sexual 

 organs and are oviparous. To this process the name 

 partlicnogcncsis, or more T^ro-^erly pscndo-parthowgcncsis, 

 is given. The products of the pseudovaria may be 

 eggs, as among the worker Bees, &c., from which 

 usually males are hatched (except in some Wasps). 

 Females with perfect sexual organs, but without the 

 stimulus of spermatozoa, may produce ova, as in the case 

 of Queen Bees, Psyche helix, Solenobia tric[uetrella, 

 and lichenella, or else embrj^os maybe produced, as in 

 some Coecidae, Chermes, &:c. 2nd. Gamogenesis is 

 that form in which the female gemmule requires the 

 stimulus of contact with the protoplasm of the male 

 spermatozoon, in order to cause its development. In 

 this case the ovum consists of a cell with a germinal 

 vesicle or nucleus, with a nucleolus or germinal spot.* 

 This is generally included within a yolk (Vitellus), 

 surrounded by a vitelline membrane. Outside this 

 are often layers of albumen and an enclosing shell. 

 There is often a micropyle or opening in the egg- 

 envelopes, whereby the contents may receive the 

 contact of the spermatozoa. On impregnation the 

 yelk shows amoeboid motion, loses its germinal vesicle 



* Within which may be n vacuole {La Valette) ox a solid briglit spot 

 {Sc7irdn). 



