116 HARLEY N. GOULD 



of a stimulating secretion thrown into the sea-water. The ques- 

 tion arose whether physical contact is necessary for the trans- 

 ference of the stimulus. 



STIMULUS WITHOUT CONTACT 



A simple apparatus (fig. 1) was devised to hold a large female 

 Crepidula at a definite distance from a small neuter without al- 

 lowing them to touch or to move farther apart. The female was 

 removed from the inner surface of a hermit crab's shell and al- 

 lowed to attach herself to the concave surface of a watch crystal. 

 The small neuter was placed on the floor of the flat-bottomed de- 

 pression in a hollow-ground slide. Mosquito netting was fas- 

 tened over the depression to prevent the neuter from escaping. 



a b c d 



Fig. 1 Diagram showing method of preventing contact between specimens. 

 a, large female; h, small neuter; c, depression slide; d, watch crystal. 



The depression slide was inverted and fastened over the watch 

 crystal containing the large female; leaving the neuter animal, 

 imprisoned in its cell, at a distance of from 4 to 7 mm. from the 

 top of the female's shell. There was no possibility of contact, 

 yet there was little hindrance to diffusion currents in the sea- 

 water between the two. The variation in the distance between 

 female and neuter was due to irregularities in the curvature of 

 the watch crystal and in depth of depression of the slide. The 

 average distance was 6 mm. 



.After various periods, samples of the originally neuter C. plana 

 were fixed and sectioned. The results are tabulated below (table 

 1). Those specimens the gonads of which showed any male de- 

 velopment beyond the mere presence of spermatogonia are marked 

 'male.' 'Inactives' are specimens with primordial germ cells 

 only, or with these plus spermatogonia. 'Females' are animals 

 where some development of oocytes could be detected. 



