316 History of British Entomostraca. 



size, but undergo various changes in colour, &c. and at the proper 

 time the ovary opens, and the young ones are ushered forth into life, 

 as unlike the parent as can well be imagined. I have already said 

 that Leeuwenhoek had noticed this difference between the young 

 and old, and upon first observing it, he seems to have been much 

 surprised at the unexpected discovery. He repeated his experiment, 

 therefore, of separating an insect with the ova attached to the tail, and 

 found the same result. " Ea hisce visis," he concludes, " certa mi- 

 ni persuasi ea animalcula, qua? jam oculis meis observabantur, ex 

 ovis illis nata esse."* He watched them for seven or eight days, and 

 found them increased in size — but here, when just on the threshold 

 of discovery, he seems to have stopped, and he makes no farther men- 

 tion of a continuation of his observations. De Geer also noticed 

 this curious fact — confirms the observations of Leeuwenhoek as far 

 as they went — gives figures of the young at different stages of their 

 growth — but stopped short in his observations also, after having 

 watched them about fifteen days. Notwithstanding this Muller 

 could not persuade himself that such dissimilar creatures could be 

 the same, and he has accordingly, without giving sufficient credit to 

 these illustrious men, or watching the hatching and progress of the 

 young himself, formed these imperfect insects into two different ge- 

 nera, which he has called Nauplius and Amymone.t Ramdohr and 

 Jurine, however, have both clearly rectified this mistake, and fully 

 corroborated the assertions of Leeuwenhoek and De Geer, by fol- 

 lowing out the transformations in all their extent. The time occu- 

 pied in this process varies much according to the season of the year, 

 and the temperature. This latter I have found produces an amaz- 

 ing difference in the length of time so occupied, and I have no doubt 

 also, from my experiments, that the process has been retarded or hast- 

 ened on, according as the vessel in which they have been kept has 

 been placed in a light or a dark situation. According to Jurine, the 

 time occupied in the case of the C. quadricornis has never been less 



* Epist. ad Soc. Reg. Ang. p. 139. 



f Entomostraca, pp. 39-48, Plates i. and ii — It is "stated by Latreille, and 

 echoed by some other writers, that the Amymone of Muller is the young of the 

 Cyclops in its earliest state, when it has as yet only four legs, and that when it 

 receives the additional pair it then becomes the Nauplius. This is not correct. 

 The different species of Amymone are the young of the C. minutus in different 

 stages, and of one or two of the marine species ; and never assume the form of 

 the Nauplius. The Nauplius (at least the N. saltatorius) is the young of the C. 

 quadricornis, which at its earliest stage resembles fig. 3 of plate 1. of Muller. 

 The N. bracteatus I have never seen, and do not know. 



