SITUS INVERSUS IN ECHINOIDS 113 



express my thanks to Dr. Mortens en for the kind permis- 

 sion to note this discovery, which ho has not yet pubhshed. 



3. Eesults of the Expekiments. 

 The purpose of our experiments made under the direction 

 of Professor MacBride was to carry out a further test of 

 the influence of high sahnity on the production of double 

 hydrocoeles (15, pp. 334-7, 341). Fresh specimens of 

 Echinus miliar is were sent from Plymouth, ripe males 

 and females were then selected from among them, and the 

 eggs were fertilized. For detailed descriptions of the method 

 we adopted I refer to MacBride's paper (15, pp. 326-9). 

 Only a few details need be added here (see table on p. 115). 

 ' Outside water ' of Plymouth (1, p. 372) was always used in 

 starting the culture, viz. the eggs were fertilized in it and then 

 kept for a day in finger-bowls filled with clean ' outside water ' 

 (' finger-bowl period '). One-day-old larvae with pyramidal 

 body and a pair of rudimentary post-oral arms were then 

 transferred to Brelfit jars, which had been filled with ' outside 

 water ' supplied with some Nitzschia (' Breffit-jar period '). 

 Then some of them were treated for several days with ' hyper- 

 tonic ' sea-water, which had been synthetically prepared 

 according to Allen and Nelson (1, pp. 369-71), and the 

 salinity increased roughly to 3-7 per cent, while others were 

 left untreated as controls. When about a fortnight old, the 

 larvae were put into plunger jars, which had been filled with 

 synthetic sea-water of normal salinity mixed with a small 

 quantity of ' outside water ' (' plunger-jar period '). The 

 results of five more or less successful cultures are here shown 

 in the table. They were offsprings of three different parents : 

 culture nos. 1 and 4 belonging to the first, nos. 6 and 9 to the 

 second, and no. 11 to the third. The larvae with the inverse 

 situs were first discovered among no. 4, on May 31. Those 

 fifty-four abnormal larvae of this culture were then kept 

 separate in a Breffit jar. On June 19, thirty days after fertiliza- 

 tion, some few among the normal ones of this culture were 

 found just metamorphosed into tiny young sea-urchins, while 



