6 University of California Publications in Zoology. VoL - 6 



aerated, died. At last I hit upon teleostian eggs that could be 

 easily manipulated. Those of the California mud-fish, Fundvius 



pam/iiii nis were used. 



It will not be too much of a digression to give a few notes on 

 the breeding habits of the fish in the interest of future work with 

 these eggs: F. parvipinnis exhibits marked sexual dimorphism. 

 The males are apt to be slightly larger than the females though 

 both sexually mature animals vary considerably in size (6.5-10.5 

 cm. for males, and 6.25-10.0 cm. for females). The females are 

 of a silvery color with no dark bars, while the males are darker 

 with brassy coloration on the fins and tail and several transverse 

 black bars along the sides of the body. In captivity at least the 

 males are cannibalistic and devour immediately any eggs laid by 

 their consorts, so it was found best to keep the sexes separated. 

 The fish are very hardy and may be kept indefinitely in aquaria 

 without difficulty. Both males and females can be easily stripped 

 and the eggs enseminated either by the dry or wet method, al- 

 though I got the best results with dry milt and believe this is the 

 method generally used in large fish hatcheries. 



The spawning season is evidently rather short. On July 8 I 

 seined in Mission Bay and took over 200 fish. With a very few 

 exceptions all were ripe and there was no difficulty in obtaining 

 eggs and milt. On July 15 I seined again. Of the 262 animals 

 taken (165 males and 97 females) with the exception of eight 

 males, none were ripe. 



The eggs are spherical, a light golden yellow in color and 

 0.28 cm. in diameter. In each egg there is a large oil drop which 

 keeps constantly at the top of the egg. Just on the edge of this 

 oil drop, or lying partially beneath it. is the germinal disc. When 

 iii-st stripped the eggs are soft and easily broken, the investing 

 membrane being thin and readily ruptured. Ten to fifteen min- 

 utes after ensemination the same eggs can be handled with a 

 pipette or even lifted with forceps and are fairly resistant. As 

 mentioned above I was unsuccessful in getting a second supply 

 of eggs. The first lot obtained bad developed until the heart had 

 begun to beat and the eye and ear vesicles were noticeable before 

 I mastered the tecbnicpie of weighing. The blastodisc had spread 

 over the whole yellow yolk mass, carrying with it droplets of the 



