114 Dr. F. Miiller on the Metamorphoses of the Prawns. 



the carapace has, besides the median spine-like process, a shorter 

 one on each side, which is directed obliquely forwards and out- 

 wards. Moreover, when at the same grade of development, it is 

 larger, and was seen as a Zo'ea as much as 2'3 mill, in length. 

 Younger Zo'ea, which still want the processes of the carapace, 

 are so like those of the former species, that it was not without 

 trouble that I learnt to distinguish them by the structure of the 

 antennae &c. Upon the median eye of this second species the 

 skin usually forms two lentiform thickenings at the sides of the 

 bacillus ; once I saw a single larger one opposite to the bacillus. 

 Between the two nervous cords of the ventral chain, a minute 

 median filament may be distinguished running from ganglion 

 to ganglion (this can hardly be wanting in the other species, 

 but has not yet been distinctly seen in them). Notwithstanding 

 its remarkable similarity to the former species, the course of 

 development is somewhat different, the third pair of footjaws 

 and the caudal appendages appearing not before, but simulta- 

 neously with the thoracic feet. 



A third species was traced from young Zoeee 1'2 mill, in 

 length, in which the new segments were still of equal length, 

 and the first rudiments of the third pair of footjaws and of the 

 caudal appendages had just been formed, up to J/y*is-like forms, 

 3 mill, long, furnished with three imperfect pairs of chelae and 

 abdominal feet. It is characterized by its being abundantly 

 armed on the carapace and the segments of the abdomen with 

 spinous processes ; the median lamina of the caudal fan is also 

 produced, in the Afysis-form, into two long points. The course 

 of development appears to be precisely like that of the first spe- 

 cies ; the form of the basal joint of the inner antenna in the 

 oldest observed larvae (fig. 10) indicates that here also an ear is 

 formed similar to that of the first species. 



Of two other species whose Zo'ea closely approach the three 

 preceding in the structure of the antennae, of the spinose upper 

 lip, of the multiarticulate second maxilla, of the tail, heart, &c., 

 one was only traced to the non-cheligerous Mysis-ioxva ; the other, 

 however, which acquires three pairs of chelae, departs so widely 

 from the rest in its mode of development, that I postpone the 

 history of its metamorphosis for the present, in order to describe 

 it separately. 



EXPLANATION OP PLATE IV. 



The figures of the animals are magnified 45 diameters ; fig. 2, 180 dia- 

 meters; and the rest, 90 diameters. The Roman numbers i.-xix. indicate 

 the appendages corresponding with the nineteen pairs of the mature ani- 

 mal : ff, flagellum of the second pair; a, outer, i, inner branch of the 

 appendages; L, upper lip; A, heart; I, liver; Z', anterior, /", median. 



