106 SURVEY OF THE REPRODUCTIVE PROCESS 



ters of the perfect insect, only their sexual development 

 being arrested. In this they contrast with those cases in 

 which the males are the subjects of arrest, as among the 

 Cirrhipedes and Lerneans ; for then it is the general organi- 

 zation that is defective, the sexual parts being developed 

 out of all proportion to the rest of the body. 



The whole development, however, of these last-mentioned 

 orders is exceedingly anomalous. The first change, induced 

 on the germ-mass of the ovum, assimilates it to the gene- 

 ral character of Entomostraceous Crustaceans, but a sub- 

 sequent transformation, of what is called a retrograde 

 character, results in the loss of vision and of the power of 

 locomotion, and so masks the articulate character that the 

 forms ultimately assumed were long referred to wholly 

 different types of organization. There is, however, another 

 possible view of such cases, which will be considered after- 

 wards. 



Throughout the articulate series, the sexes are normally 

 separate, except in some aberrant forms of the Crustacean 

 class, and perhaps also some of the lower Arachnida. 



The cases of well-marked alternation, such as occurs 

 among the Aphides, will be taken into consideration when 

 that subject comes to be discussed. 



11. VERTEBRATA. 



The remarks just made in regard to the abeyance of 

 gemmation, the absence of phenomena of alternation, and 

 the constancy of the separation of the sexes in Articulata, 

 all apply with still greater force to the Vertebrate division 

 of the Animal Kingdom ; but no farther remarks seem to be 

 called for here on the reproductive process in this group, as 

 the relation to it of various modes of propagation occurring 

 among the lower organisms has been throughout a primary 

 object of attention in this summary. 



