Page:Proceedings of the Royal Society of London Vol 60.djvu/215

Rh the gametophyte of the latter, with its reduced number of chromosomes, finds its analogue merely in the maturing sexual cells of Fucus. But until we know more of the nuclear changes as they occur in other Algae, and especially in the more primitive forms, it seems unadvisable to go further than to indicate the possibility that we may require to revise our present ideas on the comparative morphology of the higher and lower groups of the vegetable kingdom. Even if we regard the reduction in the number of the chromosomes as a fact which is primarily of physiological importance, we may safely conclude, from the universality of its occurrence, that it is also intimately connected with the phylenogenetic development of living forms, and hence it must meet with due recognition on the part of the morphologist who is engaged in comparing the life-history of one group of organisms with that of others.

In making some measurements of young male Carcinus mcenas from Plymouth, corresponding to those made by Professor Weldon on young females of the same species, and published by him in the Report of a Committee for conducting statistical inquiries into the measurable characteristics of plants and animals (‘ Roy. Soc. Proc.,’ vol. 57, p. 360), some interesting facts were observed as to changes taking place in the relative dimensions of certain parts of the carapace of these-*crabs in the space of the last three years. The carapace of the adult male crab, measured in the median antero-posterior line is, roughly, from 40 to 60 mm. long. Now, of young male C. mcenas collected at random at Plymouth in the year 1893, I had, for the purposes of measurement, 3,077 specimens, ranging between 10 and 15 mm. in length of carapace, and on these, besides the carapace length, as above defined, two other measurements were taken, viz. (1) “ frontal breadth,” the distance in a straight line between the tips of the two teeth which form the outer boundaries of the orbits, and (2). the “ right dentary margin,” measured in a straight line from the tip of the first to that of the last lateral tooth on the right side of the carapace.

The measurements were made in the way described in the Report above mentioned pp. 361—2) : and owing to the rapid growth and alteration of proportional dimensions in the young crabs, they were sorted into groups, the members of each of which differed by less than 0‘2 mm. in carapace length, thus giving five groups for