CHAPTER XXVI. 



EMBBYOLOGICAL METHODS. 



585. Artificial Fecundation. This practice, which, affords 

 the readiest means of obtaining the early stages of develop- 

 ment of many animals, may be very easily carried out in the 

 case of the Amphibia anura, Teleostea, Cyclostomata, Echino- 

 dermata, and many Vermes and Coelenterata. 



In the case of the Amphibia, both the female and the 

 male should be laid open, and the ova should be extracted 

 from the uterus and placed in a watch-glass or dissecting- 

 dish, and treated with water in which the testes, or, better, 

 the vasa deferentia, of the male have been teased. 



Females of Teleostea are easily spawned by manipulating 

 the belly with a gentle pressure ; and the milt may be 

 obtained from the males in the same way. (It may occa- 

 sionally be necessary, as in the case of the Stickleback, to 

 kill the male, and dissect out the testes and tease them.) 

 The spermatozoa of fish, especially those of the Salmonidse, 

 lose their vitality very rapidly in water; it is therefore 

 advisable to add the milt immediately to the spawned ova, 

 then add a little water, and after a few minutes put the 

 whole into a suitable hatching apparatus with running 

 water. 



Artificial fecundation of Invertebrates is easily performed 

 in a similar way. It is sometimes possible to perform the 

 operation under the microscope, and so observe the pene- 

 tration of the spermatozoon and some of the subsequent 

 phenomena, as has been done by FOL, the HEKTWIGS, 

 SELENKA, and others for the Echinodermata and other forms. 



586. Superficial Examination. The development of some 

 animals, particularly some Invertebrates, may be to a certain 



