GENERAL DIRECTIONS. 81 



following way. If a gravid specimen is kept in the aqua- 

 ria a short time the young may crawl out through the 

 genital slits and will then be found in the jar in which the 

 adult is kept. If it is desirable to hasten the parturition 

 the top of the disk of the parent may be removed and then 

 the young washed out gently with a pipette from the sacs 

 in which they are formed. 



The young of Pteraster must be searched for in the 

 grooves on the back covered by the tent-like membrane 

 which is stretched from the tips of the spine ; those of 

 Leptasterias may be found attached near the mouth. 



Asterias may be artificially fertilized and ova collected 

 in numbers by a method similar to that described for Echi- 

 narachnius. Strongylocentrotus and Arbacia can also be 

 treated with success by the same method. 



It may happen in surface fishing that a large number of 

 Coelenterata and Echinoderm larvee may be taken with the 

 dip net in the method described under the use of that in- 

 strument. This method of collecting, however, does not 

 yield the numbers, except in exceptionally good fishing 

 that one can obtain by keeping the adults in confinement 

 until the eggs are dropped or impregnated by artificial 

 methods. 



The collecting of young Coelenterata and Echinoder- 

 mata with the dip net to till out a series has one among 

 many advantages. From the fact that there is a slight 

 variation in the time of ovulation, larval stages of marine 

 animals in all conditions of growth may often be fished out 

 of the sea in the same excursion. It thus happens that, 

 for instance, in the case of the star-fish one may find the 

 stages of growth from the youngest gastrula to the brachi- 

 olaria in the same collecting trip. By the method of col- 

 lecting with a dip net it is thus possible to obtain more 



ESSEX INST. BULLETIN, VOL. XXIH 6 



