THE PLANKTON IN ST. ANDREWS BAY 5 



SESSIONAL PAPER No. 39b 



Indeed so far as the zooplankton is concerned, it is an open question whether 

 the planktonic habit is not in every case the consequence of secondary adaptation. 

 In any case it is obvious that it must be an arbitrary proceeding to select one of 

 the leading planktonic types as representing a primarily pelagic, ancestral stock. 



Two kinds of plankton are to be distinguished by their situation, namely, 

 the oceanic and the coastal or neritic* plankton. These associations naturally 

 merge into one another, but the latter is much the richer. It seems natural to sup- 

 pose that the oceanic plankton is but an expansion of the neritic plankton, just as 

 southern forms are carried northwards by the Gulf Stream, while northern forms 

 are borne southwards by the Labrador current. 



The next suggestion which might occur to the mind is one that cannot be 

 advanced definitely without a prolonged analysis; and it is only too likely that 

 even then it would fail to carry conviction. It may nevertheless be proposed as 

 a thesis that the neritic zooplankton is to be derived ultimately from the littoral 

 fauna. 



There are two kinds of large and well-known jelly-fishes or umbrella-shaped 

 medusae, several inches in diameter, which are commonly seen floating near the 

 surface in St. Andrew's bay or left stranded on the beach by the receding tide. 

 One of them is the common American Aurelia flavidula with its four horse-shoe- 

 shaped rosettes; the other is called Staurostoma laciniatum, with a simple St. 

 Andrew's cross showing through the transparent disc. The first recorded speci- 

 men of the Staurostoma was brought to L. Agassiz in a jar containing Aurelia 

 taken in Boston harbour in 1849; he says he had scarcely ever valued any dis- 

 covery more highly. 



Besides these true jelly-fishes there is another class of pelagic animals which 

 bear some resemblance to medusae from which, however, they differ in shape 

 as well as in many more fundamental characters. They are usually barrel-shaped 

 and, running lengthwise from one end of the barrel towards the other, there are 

 eight equidistant rows of vibratile, comb-shaped flappers, whence the class was 

 named Ctenophora by Eschscholtz in 1829. 



The Ctenophora are the most exquisite creatures imaginable and always 

 excite the unbounded admiration and astonishment of those who see them alive 

 for the first time. The body is generally as clear as glass, of filmy consistency, 

 and sometimes it will undergo complete liquefaction so that nothing visible is 

 left behind. They were represented in St. Andrew's bay, at the time of my visit, f 

 by a form which was described in 1849 by Louis Agassiz from examples collected 

 off the coast of Massachusetts, under the name Bolina alata. 



In this species the fluids of the body are so exactly adjusted to its conditions 

 of life, being separated from the surrounding water only by a cellular membrane 



* This is one of Professor Haeckel's useful terms; from Nerites, the son of Nereus and grandson 

 of Pontus and Gsea. It differs from littoral in that the latter term refers to the inshore bottom- 

 dwelling forms. The entire plankton of St. Andrew's bay, considered as a unit, belongs to the 

 neritic group. 



f The specimens were placed at my disposal by Dr. A. G. Huntsman to whom they were 

 familiar and who found a shoal of them at about 7 a.m. in shallow water, at the foot of the wharf 

 belonging to the Biological Station, during a very low tide on August 14th. 



