188 THE FLOATING ANIMALS 



the life-cycle in two similar forms. Specimens of all 

 such from tropical seas should be carefully preserved 

 for study by competent hands. 



Another subdivision is represented by Salpa. In 

 this, an animal which has developed from the egg, buds 

 off a chain of little Salps ; first the chain, then the 

 separate individuals are detached, become sexual, and 

 produce eggs, and the life-history begins again 

 (Figs. 154, 155). 



A second group is formed by the Hemichordata, in 

 which the notochord is only partly developed ; none 

 are planktonic, but one (Balanoglossus) has a plank- 

 tonic larva, which is not uncommon. 



Lastly, in the group Cephalochordata (Amphloxus), 

 in which the notochord extends to the tip of the head, 

 the adult, in shape rather like a fish, lies half buried at 

 the bottom, but the larvae are planktonic. 



Excluding the fish, which are the subject of a separate 

 chapter, the animals above described may be taken to 

 represent fairly completely types of the forms which 

 are likely to be captured at or near the surface. 



The next question is, how to catch them. The net 

 in ordinary use, termed a tow net, consists of the 

 frame, the net, and the tin. The frame is best made 

 as follows : From an oil-shop procure a thin 18-foot 

 length of flexible cane, such as is used to poke down 

 stopped drains ; a sharp bend in it may be taken out 

 on soaking the bend in boiling water. When straight 

 twist this up into a circle of 5 feet in diameter, and 

 lash the ends in with strong cord or copper wire. The 

 net is best made of Swiss silk (boul ting-cloth), such as 

 is used for sifting fine flour ; a useful all-round sort has 



