NOTE XIV., CHAPTER IV., p. 174. THE MORPHOLOGY OF THE CRAYFISH.

NOTE XIV., CHAPTER IV., p. 174. THE MORPHOLOGY OF THE CRAYFISH.

The founder of the morphology of the Crustacea, M. Milne Edwards, counts the telson as a somite, and consequently considers that twenty-one somites enter into the composition of the body in the Podophthalmia. Moreover, he assigns the anterior seven somites to the head, the middle seven to the thorax, and the hinder seven to the abdomen. There is a tempting aspect of symmetry about this arrangement; but as to the limits of the head, the natural line of demarcation between it and the thorax seems to me to be so clearly indicated between the somite which bears the second maxillæ and that which carries the first maxillipedes in the Crustacea, and between the homologous somites in Insects, that I have no hesitation in retaining the grouping which I have for many years adopted. The exact nature of the telson needs to be elucidated, but I can find no ground for regarding it as the homologue of a single somite.

It will be observed that these differences of opinion turn upon questions of grouping and nomenclature. It would make no difference to the general argument if it were admitted that the whole body consists of twenty-one somites and the head of seven.