114 



OVULATION AND EGG TR.'^NSPORT 



g. Strong swimming: forward swimming progression from 3 to 10 



body lengths, 

 h. Late swimming: forward progression more than 10 body lengths. 



The data for these observations may be cumulative. It would be physi- 

 cally impossible to complete the data in a matter of hours, for the stages 

 are not simultaneously available. For each observation (i. e. , each 

 specimen observed) a single record should be indicated on the following 

 chart, indicating the stage and the most advanced type of response. 

 When the record is complete, there should be a minimum of 10 observa- 

 tions (10 specimens analyzed) for each stage. 



Youngstrom (1938) has added a few, more advanced stages in response. 

 These are: 



a. The larva becomes free swimming - tactile stimuli unnecessary. 



b. Beginning of spontaneous eye movements. 



c. Body resists rotation. 



d. Hind leg buds appear. 



e. Hind leg buds become n-iotile. 



f. Beginning of withdrawal leg reflex. 



2. It is suggested that the student determine the onset of response to light stim- 

 ulation. The more highly pigmented Anura may respond earlier than the 

 lighter colored Urodela; or neither may respond to variations in light until 

 the retina develops. 



A regulation Spencer diaphragm miscroscope lamp with heat-absorbing, 

 water -filled., round bottom (500 cc. ) flask will provide an adequate spot light. 

 After proper focusing of the light onto the binocular microscope stage, turn 

 off the light and in the dim (ceiling) light of the room orient the embryos of 

 various stages within the field of the microscope. After a minute or two, 

 turn on the spot light while observing the embryo through the microscope and 

 note any reaction to the light. The embryos should be oriented toward and 

 also away from the source of light. 



3. Detwiler (1946) has devised a method of quantitating the distance travelled by 

 the individual Amblystoma larvae (stages #39 and upwards) which are normal 

 and those which have had parts of the embryonic central nervous system re- 

 moved. He found that larvae lacking the midbrain began to show a failure in 

 locomotor capacity at stage #41, and that the hemispheres were relatively 

 unimportant in the general locomotor activity of the larvae. 



An improved device placed beneath a Syracuse dish for quanti- 

 tating the distance traveled by individual Amblystoma larvae 

 (stages 39 to 46 ). The outer heavy circle corresponds to the 

 inner wall of the dish; the inner heavy circle indicates a glass 

 ring the heigiit of the disli. The space between the two repre- 

 sents a "moat" approximately 7 mm. in diameter. Each larva 

 was placed in tlic moat and stimulated twenty-five successive 

 times at approximately S-second intervals, and the total distance 

 was recorded in units (sectors of arc). The glass ring has been 

 added to the original device (Detwiler, 1945, Fig. 1), to pre- 

 vent larvae from occasionally short-cutting as they swim along 

 the wall of the dish. 



From Detwiler, 1946: Jour. Exp. Zool. 102:321. 



