SUPERFICIAL EXAMINATION. 301 



CHAPTER XXV. 

 EMBRYOLOGICAL METHODS. 



584. 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 ob- 

 tained from the males in the same way. (It may occasionally 

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

 male, and dissect^out the testes and tease them.) The sper- 

 matozoa of fish, especially those of the Salmonidae, 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 penetra- 

 tion of the spermatozoon and some of the subsequent phe- 

 nomena, as has been done by Fol, the Hertwigs, Selenka, and 

 others, for the Echinodermata and other forms. 



585. Superficial Examination. The development of some 

 animals, particularly some Invertebrates, may be to a certain 

 extent followed by observation of the living ova under the 

 microscope. This may usefully be done in the case of various 

 Teleosteans, such as_the Stickleback, the Perch, Macropodus, 



