ON THE NOMENCLATUUE OF THE SEXUAL ORGANS. 341 



d. Tlie gonads take the fonu of very numerous ellipsoidal 

 spores, each producing numerous ciliated gametes. 

 Zygote, a zygospore. AcetaciUaria, 



II. The gametes are of equal size, but one (ovum or eyg-cell) 



is either altogetlier non-motile or becomes so before 

 conjugation, while the other (sperm or sperni-cell) is 

 motile. With the differentiation of the gametes the 

 gonads may be distinguished as ovary and sperniary 

 respectively. Zygote, a zygospore. 



a. Ovum wholly non-motile : sperm amoeboid. Spirogyra. 



b. Ovum ciliated at tii'st, but coming to rest and losing its 



cilia before conjugation : sperm ciliated. Ectocarpus. 



III. Gametes dissimilar both in form and size, one the tnicro- 

 gamete, being relatively small and active ; the other, 

 or macrogamete relatively larger and passive. 



a. The gamete is co-extensive with the oi'ganism. 



a. A free-swinmiing micro-gamete conjugates with an 

 action, but fixed maci'o-gamete. The zygote is 

 active, and indeed is indistinguishable from the 

 macro-gamete, and the only result of the process is 

 increased activity in fissive multiplication. 



Vorticella. 



(3. A free-swimming micro-gamete or sperm conjugates 

 with a macro-gamete or ovum, wliich is a single 

 unicellular zooid of a free-swimming colony. The 

 zygote is an oosperm, which, by repeated fission, give 

 rise to a new colony. Eudorina, Volvox. 



b. The gamete is not co-extensive with the organism : the 



male and female gonads take the forms of spermary 

 and ovary respectively. 

 a. Ovary produces one or more macro-gametes or ova, 

 spermary one or more micro-gametes or sperms. 

 Zygote an oosperm. 



1. Ovary and spermary multicellular; sperms ciliate: ova ciliate 

 at first but come to rest before fertilization. Cutleria. 



2. Ov^ary unicellular, producing one or more ova by rejuvenes- 

 cence ; spermary unicellular, producing one or more sperms. 



i. Two or more ova to each ovary : fertilization 



extra-ovarian. Fucus, &c. 



ii. One ovum to each ovary : fertilization intra- 



ovarian. 



a. The oosperm produces the adult oi'ganism by direct 



irei'miiiation. Vaiicheria. 



