EXPERIMENTAL EQUIPMENT AND PROCEDURES 13 



MEMBRANES 



The eggs of all amphibians are surrounded by secondary (jelly) membranes secreted by 

 the oviduct in addition to the vitelline membrane. These membranes presumably protect 

 the embryo from bacteria and injury during development. Any operations on such embryos 

 require that such membranes be removed. It must be remembered, therefore, that the 

 unprotected embryo is rather easily injured and that it is more susceptible to physical 

 and chemical changes in the environment, as well as to bacterial infection. 



A. URODELA 



The Urodele jelly is rather tough and may be peeled off of the eggs with sharp pointed 

 watchmaker's forceps. The vitelline membrane will be resistant to puncturing so that it 

 may be necessary to use glass micro-needles to make the initial break. Urodele egg 

 capsules should be opened in Urodele Growing Solution. 



B. ANURA 



The Anuran egg is surrounded by loose jelly which is adherent to the vitelline membrane. 

 Attempts have been made to remove this jelly by Ultra-violet light or by dilute KCN, but 

 there is no reliable chemical method of jelly removal which allows the embryo to sur- 

 vive. Should someone discover a method of fertilizing body cavity eggs (devoid of jelly) 

 this would be a boon to experimental embryology. The Anuran egg jelly can be removed 

 to some extent by rolling the egg on filter paper or paper toweling, pushing it along with 

 the flat side of a scalpel. The danger in this method is, of course, excessive mechanical 

 injury to the egg so that the correct rate and amount of absorption (by filter paper) and 

 the exact amount of rolling will have to be determined empirically. With practice it is 

 possible to pierce the jelly with one prong of the forceps, slide a prong of a second pair 

 of forceps along the first,, and cut through the jelly with an outward movement. Then the 

 split jelly capsule can be shelled off of the egg. The enzyme hyaluronidase, so effective 

 in denuding the mammalian egg, may prove of similar value with the amphibian egg. 

 (Personal communication from D. C. Metcalfe and reference to Kurzrok 1948: Am. Jour. 

 Clin. Pathology, p. 491.) 



STANDARD LABORATORY EQUIPMENT 

 IN EXPERIMENTAL EMBRYOLOGY* 



MAJOR EQUIPMENT 



1. Water table - wood or stone table provided with current of tap water to depth of 1 

 inch to be used for holding finger bowls, etc. , at fairly constant temperatures. 



2. Refrigeration - electric refrigerators (or constant temperature rooms) with heating 

 units installed so that the temperatures may be regulated. Best temperatures are 

 4°C. , 10° C. , and 20° C. 



3. Incubators - thermostatically controlled boxes which can be regulated at tempera- 

 tures above the laboratory temperatures. Best temperatures are 25° C. ,29 C. , 

 32° C. , and 35° C. Chick incubators regulated at 103°F. for few eggs (Oaks, 

 Chicago) or for several hundred eggs (Buffalo Incubator Company, Buffalo) should be 

 on hand. 



* Note: The following list is rather exhaustive because it includes equipment needed to carry on all of the complicated procedures 

 outlined. The list is intended as a guide for the Instructor. Many of the experiments can be conducted with a pair of 

 watchmaker's forceps, a scalpel, a binocular microscope, and heat absorbed lighting. It is not necessary, therefore, to 

 provide all the items in this list in order to encourage research in experimental embryology. 



