NATURAL HISTORY OF AMERICAN LOBSTER. 1 63 



that successive annual broods are occasionally produced, as has been known to occur in 

 Homarus gammarus on the English coast, and after transplantation to New Zealand. 



In many of the prawns the eggs all hatch in the course of a few hours, and at night 

 or very early in the morning, as I have observed in Pontonia, Stenopus, and Synalpheus. 

 The adult Pontonia lives in the mantle chamber of Pinna, a large bivalve moUusk. For 

 a day or two its young move about in a dense cluster like a swarm of gnats. 



The young in most Crustacea are hatched in an immature state, and in most species 

 they cut loose from the parent at once, proceed to the surface, and as pelagic larvae 

 lead an independent existence for days or weeks. Though as adults they may be 

 sedentary and chained to the bottom, as larvae they are usually most active, and it is 

 during this period of free swimming that they undergo their metamorphosis, or series 

 of changes by which most of their proper adult characters are acquired. 



So remarkable are some of these larval changes, and so great is the difference of 

 degree in which they are expressed, even in forms so near akin as lobster, crayfish, 

 and prawn, that the fact when first affirmed was denied as incredible. The credit for 

 the discovery of the metamorphosis in Crustacea, which has proved to be a most fruitful 

 generalization in zoology, belongs primarily to a Dutch naturalist, who has not always 

 received his just dues, and secondarily to an Irish zoologist, for the old observations 

 of Martin Slabber," made June 24-28, 1768, and published with excellent drawings in 

 1778, were not followed up and fully understood until J. Vaughan Thompson confirmed 

 and completed them by studies began in 1822, continued for many years, and published 

 at various times from 1828 to 1843. The sea-waterflea or Taurus of Stier, which 

 Slabber figured and distinctly described as passing by metamorphosis to a different and 

 higher form, was afterwards regarded as representing an independent genus of animals 

 and renamed Zoe or Zoea by Bosc '' in 1 802 . 



Bell, who has given a very fair account of this subject in the introduction to his 

 work already referred to, thought that the zoea which Slabber had under observation 

 was the larva of the common ditch prawn Palcemon varians, later described by Du 

 Cane. 



Very shortly Thompson obtained in abundance larvae resembling the Zoea taurus 

 of Bosc by rearing the eggs of the common English crab. Cancer pagurus. Again in 

 1835, by extending his studies to the common green crab, Carcinus mcenas, he 

 showed that it not only was hatched as a zoea, but passed from this larval state into 

 a megalopa before acquiring the true crab-like form and characteristics, proving that 

 this mythical genus which had been proposed by Leach was, like the zoea, only a passing 

 phase in the metamorphosis of the crab. Then it was shown that in the course of its 

 development from the egg the crab passed through two consecutive stages which were 

 so unlike each other and so unlike the adult form that former naturalists had placed 

 them not only in different genera but in different families. 



a Slabber, Martinus. Natuurkundige Verlustigingen behelzende Microscopise Waarneemingen van In-en Uitlandse Water- 

 en I^and-Dieren. Waameeming van een Zee-Watervloo, genaamd Taurus of Stier, v. stukje, s plaat, p. i-xn, 1-166, pi. 1-18. 

 Haarlem, 1769-1778. 



ft Bosc et Desmarest, Manuel de I'liistoire naturelle des Crustac^s, t. n, p. 237. Paris, 1830. 



62399°— II 2 



