DEGENERATE SEXUAL REPRODUCTION. ^5 



from its host. In the fungus on the coffee-plant, for example, the stimulus of 

 ertilization is replaced as it were by an " essence of coffee." 



Male parthenogenesis, paradoxical as it sounds, is really exhibited among 

 lowly algae. That is to say, a small spore (or male-cell) which normally unites 

 with a larger and more quiescent one (or female-cell), may occasionally start 

 developing on its own resources. The result, however, is poor enough. As 

 those spores are on the border-line between asexuality and differentiated sex- 

 elements, the retention of a vegetative power of division even by the incipient 

 male-cell is not surprising. Nor must it be forgotten that the mother-sperm-cell 

 itself has a power of parthenogenetic development. It divides, like its 

 homologue the ovum, into a ball of cells, but having none of the conservative 

 coherence of the latter breaks up into spermatozoa. It is exactly comparable 

 to the interesting protozoon (Magosp/ia-ra) which Haeckel saw, which did its 

 best to get beyond the Protozoa, but failed as soon as it had succeeded. A 

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

 coherence and broke up into infusorians once more. 



V. 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 :— 



1. 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 uncertein result (for example, Silkmoth). 



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



example, Bees). 



3. Mostly males, with occasional females (for example, Nematus). 



4. Mostly females, with exceptional or periodic males (for example, Apus, 



Artemia). 



5. Only female, males unknown (for example, many Rotifers.) 



That parthenogenetic ova should develop with such diverse results is not at 

 all surprising. The absence of fertilization 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 :— 



Example. 



Most organisms. 



Rarities mentioned. 



Many insects. 



Hive-bee and some 

 other forms. 



Nematus (allied to bee). 



Most gall-wasps. 



Some sawflies. 



Some water-fleas. 



Solenobia sometimes. 



Aphides ; some water- 

 fleas. 



Many water-fleas. 



Most rotifers. 



Many rotifers. 



p 



> 



•O 



y 



W 



w 

 o 

 o 



w 



a 



H 

 Of! 

 < 



Result. 



Nil 



Partial and pathological development 

 Great mortality in a mixed brood 

 $ 's alone 



$ 's mostly, a few 9 ' s 

 <?'s and 9's (one generation'. 

 \ $'s, and more than a few 9 's 



9 9 9 (a succession), then a predominance of $ 

 999, then equal numbers of $ 's and 9 's 

 999, then a minority of £ 's among 9 's 



9999, very rare $ 's 



9 9 9 9, non-functional <y's among 9's 



9 9 9 9, ad infinitum, no $ 's 



