538 LIFE : OUTLINES OF GENERAL BIOLOGY 



of two sets of investigations by Mr. J. T. Cunningham and by 

 Nansen (who was long a productive zoologist). 



Specimens below a certain size are said to be all males; those 

 above a certain size, about a foot, are said to be all females. This 

 means that as the hagfish grows to maturity, its unpaired repro- 

 ductive organ changes from being a sperm-producer to being an 

 egg-producer. 



There is a little starfish {Asterina gibbosa), found in European 

 waters, which is first male and then female, with an interesting 

 intermediate phase when it is both, or, in other words, a transient 

 hermaphrodite. This is a very interesting case which deserves 

 further study. Even by itself it is enough to show that sex is not 

 necessarily a rigidly fixed constitutional state, but rather a physio- 



FlG. 80. 



Group of Slipper Limpets {Crepidula fornicata), one on the top of another. 

 After Orton. SH, the basal .shell; A, B, C are female; D is a hermaph- 

 rodite; H, F, G are males. 



logical phase, to .some extent plastic and even capable of swinging 

 to the other extreme. 



Very extraordinary is the story of a limpet-like animal called 

 Crepidula which has been introduced into English waters from the 

 United States, and has been carefully studied at Plymouth by Dr. 

 J. H. Orton, as well as by Conklin and by Gould, two American 

 zoologists. The actively locomotor young forms are males, but after 

 they .settle down on oy.ster-shells, or the like, they become hermaph- 

 rodites or neutrals. Later on they become females. In some 

 species they have the habit of fixing themselves on others of the 

 same kind, so that there may be seven individuals, one on the top 

 of another, the lowest and oldest being fixed to a shell. It looks as 

 if they had borrowed an idea from the American skyscrapers. 



Of the seven, to take one of Dr. Orton 's ca.ses, the youngest three 

 may be males, the fourth a hermaphrodite, and the oldest three 



