DEGENERATE SEXUAL REPRODUCTION. 



177 



single infusorian-like cell divided into a ball of cells, Lut 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 : — 



(i.) 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 : — 



(i.) 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. 1 Example. 



O 



o 



w 



o 

 o 



[Nil 



Partial and pathological development 

 Great mortality in a mixed brood. . 

 i 's alone ...... 



i 's mostly, a few ? 's . 



6 's and 9 's (one generation) 

 i 's, and more than a few ? 's 

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

 ance of c? 's 

 9 ? 9 , then equal numbers of i 's and 9 's 

 9 9 9 5 then a minority of i 's among 9 's 



9 9 9 9, very rare (5 's 

 9 9 9 9, non-functional i 's among 9 's 

 19 9 9 9 , ad infinitum, no c? 's 

 § 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 



I Most organisms. 

 I 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. 

 JNIany rotifers. 



parthenogenesis is 



among water-fleas 



else it affects, it is 



aphis will continue 



