There is a good deal of discrepancy between different observers as to the frequency of the process of ecdysis in crayfishes. In the text I have followed M. Carbonnier, but M. Chantran (“Observations sur l’histoire naturelle des Écrevisses:” Comptes Rendus, LXXI. 1870, and LXXIII. 1871), who appears to have studied the question (on the “écrevisse à pieds rouges” apparently) very carefully, declares that the young crayfish moults no fewer than eight times in the course of the first twelve months. The first moult takes place ten days after it is hatched; the second, third, fourth, and fifth, at intervals of from twenty to twenty-five days, so that the young animal moults five times in the course of the ninety to one hundred days of July, August, and September. From the latter month to the end of April in the following year, no ecdysis takes place. The sixth takes place in May, the seventh in June, and the eighth in July. In the second year of its age, the crayfish moults five times, that is to say, in August and in September, and in May, June, and July following. In the third year, the crayfish commonly moults only twice, namely in July and in September. At a greater age than this, the females moult only once a year, from August to September; while the males moult twice, first in June and July; afterwards in August and September. The details of the process of ecdysis are discussed by Braun, “Ueber die histologischen Vorgänge bei der Häutung von _Astacus fluviatilis_.” Würzburg Arbeiten, Bd. II. NOTE V., CHAPTER I., p. 39. REPRODUCTION IN CRAYFISHES. The males are said to approach the females in November, December, and January, in the case of the French crayfishes. In England they certainly begin as early as the beginning of October, if not earlier. According to M. Chantran (Comptes Rendus, 1870), and M. Gerbe (Comptes Rendus, 1858), the male seizes the female with his pincers, throws her on her back, and deposits the spermatic matter, firstly, on the external plates of the caudal fin; secondly, on the thoracic sterna around the external openings of the oviducts. During this operation, the appendages of the two first abdominal somites are carried backwards, {351} the extremities of the posterior pair are inclosed in the groove of the anterior pair; and the end of the vas deferens becoming everted and prominent, the seminal matter is poured out, and runs slowly along the groove of the anterior appendage to its destination, where it hardens and assumes a vermicular aspect. The filaments of which it is composed are, in fact, tubular spermatophores, and consist of a tough case or sheath filled with seminal matter. The spoon-shaped extremity of the second abdominal appendage, working backwards and forwards in the groove of the anterior appendage, clears the seminal matter out of it, and prevents it from becoming choked.