FREE BOOKS

Author's List




PREV.   NEXT  
|<   122   123   124   125   126   127   128   129   130   131   132   133   134   135   136   137   138   139   140   141   142   143   144   145   146  
147   148   149   150   151   152   153   154   155   156   157   158   >>  
the second larval stage, which is oval in form, and not segmented, the primitive band is formed. In concluding the account of his remarkable discoveries, Ganin draws attention to the great differences in the formation of the eggs and the germs of these parasites from what occurs in other insects. The egg has no nutritive cells; the formation of the primitive band, usually the first indication of the germ, is retarded till the second larval stage is attained; and the embryonal membrane is not homologous with the so-called "amnion" of other insects, but may possibly be compared with the skin developed on the upper side of the low, worm-like acarian, Pentastomum, and the "larval skin" of the embryos of many low Crustacea. He says, also, that we cannot, perhaps, find the homologues of the provisional organs of the larvae, such as the singularly shaped antennae, the claw-like mandibles, the tongue-or ear-like appendages, in other Arthropoda (insects and Crustacea); but that they may be found in the parasitic Lernaean crustaceans, and in the leeches, such as Histriobella. He is also struck by the similarity in the development of these egg-parasites to that of a kind of leech (Nephelis), the embryo of which is provided with ciliae, recalling the larva of Teleas (Fig. 197 _B_, _C_), while in the true leeches (Hirudo) the primitive band is not developed until after they have passed through a provisional larval stage. This complicated metamorphosis of the egg-parasites, Ganin also compares to the so-called "hyper-metamorphosis" of certain insects (Meloe, Sitaris, and the Stylopidae) made known by Siebold, Newport and Fabre, and he considers it to be of the same nature. He also, in closing, compares such early larval forms as those given in figures 193 _E_ and 194, to the free swimming Copepoda. Finally, he says a few words on the theory of evolution, and remarks "there is no doubt that, if a solution of the questions arising concerning the genealogical relations of different animals among themselves is possible, comparative embryology will afford the first and truest principles." He modestly suggests that the facts presented in his paper will widen our views on the genetic relations of the insects to other animals, and refers to the opinion first expressed by Fritz Mueller (Fuer Darwin, p. 91), and endorsed by Haeckel in his "Generelle Morphologie," that we must seek for the ancestors of insects and Arachnida in the Zoea fo
PREV.   NEXT  
|<   122   123   124   125   126   127   128   129   130   131   132   133   134   135   136   137   138   139   140   141   142   143   144   145   146  
147   148   149   150   151   152   153   154   155   156   157   158   >>  



Top keywords:
insects
 

larval

 

parasites

 
primitive
 

called

 

leeches

 

developed

 

provisional

 

metamorphosis

 

relations


formation

 
compares
 

Crustacea

 
animals
 
theory
 

remarks

 

Copepoda

 

Finally

 

evolution

 

swimming


figures

 

Siebold

 

Newport

 

Stylopidae

 

Sitaris

 
complicated
 

considers

 

nature

 

closing

 

Darwin


Mueller

 

genetic

 
refers
 

opinion

 

expressed

 

endorsed

 

Haeckel

 

ancestors

 

Arachnida

 

Generelle


Morphologie
 
genealogical
 

solution

 

questions

 

arising

 
comparative
 

embryology

 
presented
 
suggests
 

modestly