378 On the Development of the Crustacean Embryo. [Mar. 9, 



into the earlier stages in the development of the embryo, and comparing 

 the progress within the ovum of some of the larvae that arrive at or near 

 maturity before being hatched, with those of the larval, forms that are 

 hatched in a more immature condition ; and he states that, as soon as 

 the protoplasm assumes any thing like a definite plan, distinct lobes, cor- 

 responding in position with those of the several appendages in theNauplius, 

 together with an embryonic or ocular spot, are present; that in the if awplim 

 forms they exist as deciduous appendages only, and are soon cast aside 

 and replaced by others more adapted to the wants of the adult exist- 

 ence. 



In the embryos of other Crustacea the anterior pair of lobes enlarge in 

 size with little alteration of form, while the posterior two pairs are de- 

 veloped into appendages that have but a deciduous value, since they never 

 fulfil the office of permanent organs, and are generally cast off with an 

 early moult. 



This is observable within the ovum in Palwmon, Crangon, &c, and also 

 in the marsupial embryo of Mysis after it has quitted the ovum. 



The relation of these parts to the permanent organs the author has 

 closely traced, and believes that he has demonstrated that the three pairs 

 of mobile appendages in the cirripedal or JSfauplius form of larva homolo- 

 gize with the eyes and two pairs of antennae, and not with the antennae 

 and mandibles, as stated by Eritz Miiller, Anton Dohrn, and others. 



The author, moreover, contends that the small pair of filamentary 

 appendages seen on each side of the ocular spot, existing in the Nauplii 

 of Cirripedes, homologize with the peduncular appendage existing in the 

 larva of Caligus, the arm-like appendages in the pupa-stage of Cirripedes, 

 the peduncle of the stalked Cirripedes, and probably also with the long 

 multiarticulate, antenna-like organs belonging to the fossil Pterygotus. 



He also demonstrates the origin of the nerves in a mass of cellular 

 material that reaches from one extremity of the embryo to the other. 

 This divides into parts corresponding to the various somites into which 

 the animal divides. These masses gradually separate from each other 

 as the animal increases in size, and concentrate into the several ganglia 

 that form the great nervous chain. 



The author also shows the origin of the permanent organs of vision, 

 and the manner in which the number of lenses increases with the growth 

 of the animal, and traces the origin of several of the internal viscera 

 and their mode of growth. 



He also figures, in minute detail, the larvse of the following genera 

 (those in italics are from British specimens, while all the others are 

 from the collection sent to him by Mr. Power) : — 



"Palmmon fluvialis, n. sp. Alphceus obesimanus, Dana. 



squilla, Leach. Homaralpkseus, n. g. 



Crangon vulgaris, Leach. Homarus marinus, Leach. 



Hymenocera, Heller. Palinurns vulgaris. 



