158 Prof. M'Intosli's Note$ from the 



warm Mediterranean waters. Environment wonld thus 

 appear to be a factor of importance in some instances, if not 

 in all. Moreover, it would seem to be as unnecessary to 

 place the weight given by some authors on the presence or 

 absence of an operculum as to separate like species of oxen 

 by the presence or absence of horns. Some, like Clapar^de 

 and Fauvel, perhaps, might be disposed to separate as 

 distinct species those with and those without an operculum, 

 or to regard either as a sudden and an important mutation 

 in a given series. It may, indeed, be asked why Filograna, 

 with such a tendency to variation in the organs mentioned, 

 as well as in reproduction, has not developed along the lines 

 indicated and produced descendants in which each variation 

 fitted it to survive more readily than its fellows — whether 

 as regards its somatic cells or its germ-cells, both of which 

 are affected ? The continuity of the germ-plasm does not 

 appear to restrict the variations indicated, even in repro- 

 duction, since there may be free ova, internal embryos, or 

 buds. A study of karyokinesis in the sexual cells might, 

 perhaps, aid in solving the problem, though this is 

 conjectural. 



Again, the variability in the number of the anterior 

 (thoracic) bristles is a feature seen in not a few Polychsets 

 — for instance, in the Sabeilids. In Potamilla reniformis, O. 

 F. M., the anterior bristles may range from five to twenty- 

 six pairs, a much wider variation than in Filograna. Certain 

 races oi Filograna have seven pairs, others from seven to nine, 

 whilst the Neopolitan types may reach ten. Such is not 

 necessarily the effect of age, but rather of environmental 

 conditions — for example, the general temperature of the 

 surrounding water, the rich supply of nourishment, and the 

 abundance of light. 



In considering the differences in structure presented by 

 Filograna the variations in the tips of the branchiae occur 

 under such diverse conditions, as well as on precisely the 

 same site and under the same conditions, that one is at a 

 loss to say wherein the process of selection and the "" struggle 

 for existence" lie. Their tubes give the necessary pro- 

 tection, so that the species can vary in any manner in which 

 its inherent capacities permit, and a single generation may 

 afford examples of change in the organs referred to. The 

 enlarged tips of the branchiae are of a glandular character, 

 and thus differ from the opercula — though borne by the 

 same parts. ^Moreover, it cannot be said that disuse has 

 caused the disappearance of the opercula, since the forms 

 devoid of them have as much need of them as before. The 

 blight pigment of the branchiae shows that light, as well as 



