144 C. E. Lucas 



abundance of dinoflagellates in the water (with the postulate that this is mediated by 

 a by-product) and the subsequent hint (Miazaki, 1938) of the effect of an alga upon 

 the spawning of the male oyster. Now, Collier and his colleagues, at Galveston, 

 Texas, have moved into this field from a rather different angle. Whilst studying the 

 effects of industrial wastes on oysters, they deduced a generalized influence upon their 

 pumping rates, which was found in due course to be correlated with the presence or 

 absence in the water of a carbohydrate-like substance; this is either truly soluble or 

 colloidal, and may attain densities in neritic waters of up to 25 mg/1 (Collier, Ray, 

 Magnitski and Bell, 1953). During further work (Collier, 1953) they found that, 

 along with tyrosine-tryptophane, these carbohydrates have a marked diurnal variation 

 in abundance, and their production is associated with light and aeration — so that 

 they are probably the by-products of plant growth. In addition, a rhamnoside 

 (Wangersky, 1952) has been isolated from oceanic water, and particularly from 

 " red tide " water up to quantities of 50 mg/l, whilst minute quantities of ascorbic 

 acid and some other carbohydrates of very low molecular weight are being isolated 

 for identification. The significance of such substances to the oyster may be two-fold, 

 but it is at least clear that one of the substances in question is both widespread and 

 very variable in quantity, and that it acts as a remarkably effective (and almost 

 instantaneous) pumping stimulus. It would appear that the substance is also absorbed 

 by the oysters (up to 50 mg per hour), although it remains to be seen whether such 

 substances are of positive and substantial food value (see, for example, Korringa, 

 1949, and Jorgenson, 1952) — a possibility which would greatly have interested both 

 PiJTTER and Krogh — or whether their role is limited to providing sensory stimuli and 

 perhaps growth factors. At the moment, the chief point is that they " found a 

 biologically active compound (or group of compounds) to which an organism would 

 respond quantitatively ", and drew attention to the link between this work and the 

 probable significance of external metabolites or " ectocrines ". 



Work being undertaken by Wilson, at Plymouth, is also relevant. For many 

 years he has been concerned with the problems of breeding and growing planktonic 

 larvae, particularly polychaetes. On the one hand he noticed that sands from some 

 areas were more suitable for the settlement of polychaete larvae than others (e.g. 

 Wilson, 1948 and 1953) whilst, on the other hand, he found that, with the passage 

 of years, his success with rearing these and other larvae was tending to decrease 

 (Wilson, 1951). Continued and painstaking investigations in various directions now 

 seem to make it clear, however, that the suitability of sands for larval settlement 

 must be determined by the existence on them of other forms of life, probably micro- 

 organisms — " Organic material, living or dead, on the sand grains plays an important 

 role in rendering a sand attractive or repellent to the larvae " (Wilson, 1954). Whilst 

 we may not be so obviously concerned here with a free metabolite (although that is 

 quite possible), we have to deal once again with the significance for living larvae of 

 organic remains, and with their detection by these larvae. 



The other instance is of even more direct interest. Wilson associated his decreasing 

 success with the now familiar change known to have taken place whereby the waters 

 of the English Channel have been much less productive since 1930 than in the 1920s. 

 Superficially, this was due to reduced phosphate content, but the possibility of more 

 subtle factors remained, and comparative experiments were made by rearing poly- 

 chaete and echinoderm larvae in (a) " local " Channel water collected in the Plymouth 



