DEVELOPMENT OE CIRKIPEDIA. 
143 
mens which have already got four movable spines, and I have no doubt also in those 
with five and six spines. At first I thought that these segments and their appendages 
were indeed the future pleopods of the Cypris ; but I found no traces of these Nauplii 
being otherwise prepared for the great change, indications which are invariably only to 
be found in those larvae which are provided with six movable spines. 
The underlying spines are therefore nothing but the future six large spines of the 
adult Nauplius. 
How the pleopods develop hi this latter stage before the change into the Cypris 
form takes place I do not know, having never been able to find a Nauplius in which 
they were clearly visible underneath ; but judging from what we have seen in other 
Cirripedia, and from what we know about the development of the large spines, I have 
no doubt that they develop very much in the same way as these. 
Although a certain segmentation under the Nauplius- skin cannot therefore be denied 
in the course of the development of the larva, no trace of this is visible as soon as the 
underlying skin becomes the external one, and the Nauplius of Lepas fascicularis never 
shows on the outside any segmentation in its tail. The movable spines simply mark 
the place where, later on, we find the segmented abdomen of the Cypris . 
On our southern cruise, when we get into the regions of Lepas australis , I shall take 
up this subject again, and will make sure about this point, which is the only one of any 
consequence in the development of Lepas fascicularis which I have not quite been able 
to clear up. 
The three appendages of the adult Nauplius have been, as I have said, very accurately 
described by Dohrn in his “ Arcliizoea ,” except that he has considered the third pair to 
be the second, and vice versa. 
The first antennae are simple, with only one branch and six joints (Plate 12. fig. 15, a). 
On the first three joints there are no hairs, but on the second and third a few small 
spines may be seen, which have not been described in the southern larva. The fourth 
segment is the largest in both species ; it has three long hairs on one side and one on 
the other. The last two segments are very small, the fourth with two, and the fifth 
with three long hairs. 
During the metamorphosis of the Nauplius into the Cypris stage this is the only pair 
of appendages which remains ; and in old Nauplii you may already find stages in which 
the sucker is being developed within. I have represented, in Plate 14. fig. 22 a , a 
stage in which a large number of nucleated cells is contained in the very much enlarged 
fourth segment, showing that something is going to be formed within (fig. 22 a , 4, 
acet ). In the same figure traces of the two large joints of the Cypris- antenna may be 
seen, one of them being already visible in the first and second segment underneath the 
skin, and the second (the one that will have the sucker at the top) being formed inside 
the third and fourth. The last two segments have very much the same shape in the 
Cypris which they had in the Nauplius, only the number of hairs and set® at the top 
differs considerably in the two stages. 
