GENERAL DIRECTIONS. 79 



for in the waters near by it is more common than else- 

 where. The days following a violent storm almost cer- 

 tainly find Revere Beach strewn with multitudes of Cau- 

 dina arenata. Leptosynapta is abundant in the littoral 

 zone in front of the large hotel at the Point of Pines, but 

 it must be dug out of the sand for it lives buried in the beach. 

 I have never discovered a good locality where more than 

 a few specimens of Cucumaria can be found on a single 

 collecting trip. 



A few special hints in regard to collecting ova and 

 younger larval stages may have some value. 



A means of obtaining the free Medusae of the Hydroida 

 is to keep the attached hydroid in an aquarium until the 

 zooids are dropped. In that way, if successful, a large 

 number of individuals may be obtained, but the collector 

 must beprepared to meet with many failures, for most of the 

 hydroids are not hardy, and the laws 1 which determine the 

 time when individual hydroids mature their zooids are not 

 easily formulated. Obelia, Campanularia, Syncoryne, and 

 Clytia are good genera to use in endeavors to raise the 

 zooids. 



Artificial fecundation may in some cases be resorted to 

 for an abundant supply of the young of several of the 

 New England Coelenterata and Echinodermata. While it 

 will probably be found that a majority of the genera com- 

 posing these groups can be successfully reared in this way, 

 up to the present time only a lew have been experimented 

 upon with satisfactory results. 



1 Various circumstances probably retard or accelerate the rate of growth of the 

 young of the Coelenterata and Echinodermata. One of the most important is, pos- 

 sibly, difference of temperature. As the temperature rises Ophiopholis eggs ma- 

 ture more rapidly, and pass through their segmentation and larval conditions more 

 quickly, and the same may also be the case with many other genera. Various other 

 conditions, as amount of food, also have an important influence on the time of ov- 

 ulation and the rate of growth of larvae, so that until these facts are better known 

 it is not possible to understand completely the laws governing periodicity of ovu- 

 lation and growth. 



