194 report — 1878. 



especially Milne-Edwards, Latreille, and Westwood, as the idea of any 

 metamorphosis in the development of the Crustacea was contrary to 

 preconceived opinions, and to the careful and very complete observations 

 of Rathke on the development of the embryo in the common crayfish of 

 Europe (Astacus fluvialis) . 



The articles of Milne-Ed wards in the 'Dictionnaire Classique d'Histoire 

 Naturelle, and the remarks of Latreille in the ' Cours d'Entomologie,' 

 were followed in 1835 by what appeared at the time to be an exhaustive 

 discussion of the subject by Mr. Westwood. His observations were 

 carried out upon the ova of some land crabs, that were living in the 

 Zoological Gardens, with an exactitude and care that has left little to be 

 added. Mr. Westwood's memoir was published in the ' Philosophical Trans- 

 actions of the Royal Society,' and he received the honour of the Society's 

 gold medal for what, at the time, appeared to be a complete refutation of 

 Mr. Vaughan Thompson's theory of metamorphosis in Crustacea. 



It is, however, a very remarkable coincidence, that the same volume of 

 the 'Philosophical Transactions,' 1835, that contains Mr. Westwood's com- 

 munication on the absence of any morphology in the progressive develop. 

 ment of the Gegarcinus, also published a memoir of Mr. Vaughan Thomp- 

 son on the larva of the Cirripedia, showing not only that a very extensive 

 form of morphology takes place, but demonstrating conclusively that they 

 are crustaceous animals, and bear no relation to the mollusca among which 

 they previously had been generally classed by naturalists. 



From this time until the present, the young form and development of 

 these animals have been of the foremost interest in marine zoology. 



In 1839 Capt. Du Cane sent to the British Association, and pub- 

 lished in the ' Annals of Natural History,' a communication on the forms 

 in which the young left the egg in the common prawns and shrimps of our 

 coast. And soon after (1852), Mr. R. Q. Couch gave an account at the 

 Dublin Meeting of the British Association of the form in which the 

 young left the ovum in the common crawfish (Palinurus vulgaris) of our 

 seas. In each of these the form so differed from one another, and from 

 any of the others, that it began to appear as if the young of every genus 

 in the Crustacea left the egg in a larval form, different in character. 



This view appears to receive much strength from the development of 

 the larva in Mysis, although many of the changes which this animal 

 undergoes are those of a subembryonic rather than a larval condition, 

 since they take place pi-eviously to the animal's becoming an independent 

 creature. An elaborate account of the development of this animal is 

 o-iven by Van Beneden, in his memoir on the littoral animals of Belgium. 



Since then, the crowning interest was given by Dr. Fritz-Muller, when 

 he captured a small crustaceous animal in the high seas which in general 

 form corresponds with the small entomostracous genus known as 

 Nauplius. This he prononnced to be the early condition in which some 

 of the prawns, and especially Penasus, quits the ovum. Some naturalists 

 accept this hypothetical discovery as conclusive, while others more 

 cautiously consider that the evidence Fritz-Muller has received is not 

 sufficient, the more especially since several genera of prawns are known 

 to quit the ovum in a more advanced form. (PI. V., fig. 1.) 



It should be remembered in the reporting on this discovery of Fritz- 

 Miiller, that first it has not been taken in connection with the parent, 

 second, that it has not been traced from the nauplius to the zoaea con- 

 dition, and lastly, has not been traced by Midler beyond the Schizopod 



