CROWDING AND SEX DETERMINATION 293 



and then are carried along as free-swimming larvae, there is less 

 tendency toward male development than is shown by other larvae 

 left longer on the proboscis. However, the sex determination in the 

 attached larvae is very rapid, and in a few hours can progress far 

 enough to produce intersexes. In one experiment 16 larvae left on 

 the proboscis for between 3^ to 8 hours after attachment showed no 

 complete females, 2 slightly female intersexes, 2 male hermaphro- 

 dites, and 12 complete males. 



Experiments with stains show that male characteristics begin to 

 appear at the anterior end and gradually spread through the body 

 (Baltzer, 1928a). Larvae which have been left for several hours on 

 proboscides dyed blue and then transferred for 2 or 3 days to pro- 

 boscides colored with a red stain, show the blue limited to the ante- 

 rior part and the red distributed over the whole body. So with the 

 male-determining substance, a smaller quantity gives a narrower 

 action radius while a longer attachment with more absorption acts 

 over the whole body. 



When larvae are experimentally reared in vessels lacking females, 

 and when those starting to change in the female direction are re- 

 moved, it is found that the great majority of the animals become 

 females but that those transforming near the end show intersexual- 

 ity, including even spermatogenesis. Under similar conditions 

 Herbst (1928) found male development to be brought about by 

 the use of a weak solution of HCl; the best results were obtained with 

 an N/400 solution. In these experiments not all larvae transformed 

 into males. This observation of Herbst may account for the occa- 

 sional transformation in the male direction in Baltzer's experiments 

 just recorded. 



When larvae are reared in the presence of older females, or in the 

 presence of female proboscides, the majority of the larvae settle 

 upon the proboscides and develop into males. Similarly, extracts 

 of proboscides or of intestinal issue of females placed in sea-water 

 with the indifferent larvae bring about male differentiation. Ex- 

 tracts from muscle tissue made in the same manner did not have 

 this effect. Extract of intestinal tissue gave better results than 

 did that from proboscides, but in both instances there was slower 



