8 HARLEY N. GOULD 



will interfere with this extension of the mantle, b) Cramped 

 quarters will hinder or prevent it. 2) The amount of growth 

 varies according to the season of the year. 



D. Variations in motility of males 



Males and other small individuals of C. plana are usually 

 more motile than the large females (Conklin, '98). The writer 

 has found many exceptions to this rule, however. Occasionally 

 males are found immovably fixed. They are either wedged be- 

 tween two large individuals, or between a large one and an 

 angle of the hermit shell, or they are placed on top of larger in- 

 dividuals where the irregularities of the surface of attachment 

 were mirrored by the irregularities in the shells of the males. In 

 all these cases the shell of the male was so conformed to the 

 surroundings that there was no doubt of its having remained 

 motionless during the growth of the shell. That they were func- 

 tional males was confirmed by sections through the gonad of 

 several of them. One small animal, which, as will be explained 

 in a subsequent paper, was developing the male phase under 

 experiment, remained for several weeks in the same position on 

 top of the shell of a female, and in the meantime its own shell 

 grew somewhat and fitted itself to the irregularities of the sur- 

 face beneath it. The majority of maleg are undoubtedly motile 

 however. In Crepidula fornicata the mature males in the 

 'chains' described by Conklin and Orton (see below) are com- 

 pletely sedentary. 



E. Variations in sexual development 



There is a peculiarity of Crepidula plana, already mentioned 

 by Conklin ('98), which is as follows: Many individuals of this 

 species are found, of the same sizes as the males, which do not 

 exhibit the male condition. Neither do they yet show any indi- 

 cation of assuming the female phase. They are what may be 

 called 'sexually indifferent' or 'neuter' animals. The gonad is 

 rudimentary and resembles that of the very small and evidently 

 immature specimens. The penis, sperm groove and seminal 



