DEGENERATE SEXUAL REPRODUCTION. 



^77 



single infusorian-like cell divided into a ball of cells, but the ball had no 

 coherence and broke up into infusorians once more. 



§ 5. The Offspring of Parthenogenesis. — The fate of parthenogenetic 

 ova is very diverse. They may all perish, or all succeed ; they may turn 

 out wholly males or wholly females. Hensen notes the following suggestive 

 series, with decreasing reproductive, as opposed to constitutional, energy 

 at each level : — 



(l.) Hermaphrodites, then only females. 



{2.) Series of females, then mixed brood. 



(3.} Several females, mixed brood, then only males. 



(4.) Series of mixed broods, then males, or death of ova. 



{5.) Mixed brood, with much mortality. 



(6.) Males only. 



(7.) Development only for a few stages. 

 Rolph has a different arrangement, but the same idea : — 



(1.) Exceptional parthenogenesis with uncertain result (^.^., Silkmoth). 



(2.) Normal, producing males only (female solely from fertilised ova) 

 {e.g.. Bees). 



(3.) Mostly males, with occasional females {e.g., Nematus). 



(4.) Mostly females, with exceptional or periodic males {e.g., Apus, 

 Artemia). 



(5.) Only female, males unknown {e.g., many Rotifers). 



That parthenogenetic ova should develop with such diverse results is 

 not at all surprising. The absence of fertilisation removes one of the 

 factors determining sex ; but food, temperature, age of ovum, &c., remain, 

 and produce bias now to one side, now to the other. To this we shall 

 presently return ; meanwhile the facts of offspring may be more clearly 

 expressed thus : — 



Result. Example. 



O 

 u 



'^ 

 ux 

 o 

 o 



IS 



K 

 H 

 Pi 

 < 



'Nil . . . . 

 Partial and pathological development 

 Great mortality in a mixed brood. . 

 i 's alone ...... 



i 's mostly, a few ? 's . 



cJ 's and 9 's (one generation) 

 (J 's, and more than a few ? 's 

 9 9 9 (a succession), then a predomin- 

 ance of (5 's 

 9 9 9, then equal numbers of 6 's and 9 's 

 9 9 9, then a minority of i 's among 9 's 



9 9 , very rare (5 's 



9 9 , non-functional 6 's among 



9 9 > ad infinitum, no cJ 's 



9's 



9 9 

 9 9 

 19 9 



§ 6. Effects of Parthenogenesis. — Since 

 dominant in rotifers, and well established 

 and plant-lice, it is very plain that whatever 

 anything but prejudicial to numbers. An 



M 



Most organisms. 

 Rarities mentioned. 

 Many insects. 

 Hive-bee and some 



other forms. 

 Nematus (allied to 



bee). 

 Most gall- wasps. 

 Some saw-flies. 



Some water-fleas. 

 Solenobia sometimes. 

 Aphides ; some water- 

 fleas. 

 Many water-fleas. 

 Most rotifers. 

 Many rotifers. 



parthenogenesis is 



among water-fleas 



else it affects, il is 



aphis will continue 



