DEVELOPMENT OE CIKRIPEDIA. 
139 
The young Nauplius is now in full vigour, evidently taking in plenty of food and 
rapidly growing. Every time it moults it gets one more movable spine on the tail 
(Plate 12. fig. 15, sp 1 ), on which there is, a little lower down, another large curved 
spine ( sp 2 ), and lower down still a straight one, besides a number of small and middle- 
sized spines. In the full-grown Nauplius (the carapace of which has a diameter of 
2 millims., and the larger spines are 12 millims. long) there are six movable pairs of 
spines on the tail. It gets these only after the fifth moult, the last it has to 
undergo in the Nauplius stage of its life. The number of spines is the chief test of 
its age, and will be found to correspond exactly to its size. When in possession of three 
or four of them it is only half the size of one which has six. After this, however, it 
in most cases gets six spines at once. I have figured in the accompanying Plates two 
stages — one with four and the other with six spines, and have represented in each of 
these figures different organs so as to show its anatomy without crowding them 
too much. In giving a description of the Nauplius in the adult stage, I shall of 
course frequently refer to the “ Archizoea gig as” but must first mention that Dohkn, 
though his figures of the three appendages are excellent, has evidently taken the second 
for the third appendage, so that in comparing our drawings with each other this must 
he borne in mind. When I remarked it, I looked at the Nauplii of both species again, 
to see whether I had not perhaps myself made the mistake (which, as one separates 
the appendages from the body, is very excusable) ; but I found that certainly my 
drawings are correct, and that of all the appendages the second (as is also the case in 
the Nauplii of several other Cirripeds which I have studied) are the largest. 
The carapace of this Nauplius has the form of an hexagonal cover, with a very long- 
handle to it springing from its middle, which is a little raised (Plate 10. fig. 12). 
Besides the central spine there are on the carapace two posterior lateral processes, two 
processes in front of the eye between the horns, six large processes (one at each angle 
of the hexagon), and several smaller spines (two to four) between each pair of these. 
Altogether there are on the carapace one dorsal spine, two lateral horns, eight larger, 
and from twenty-five to thirty smaller processes, all of which, with the exception of the 
spine, have a gland opening at the top. 
In “ Archizoea gig as ” there are also eight large processes [vide Dohrn’s fig. 1 on 
tab. 28, l. c., and my fig. 23 on Plate 14) with glandular openings ; but besides there 
are a vast quantity of very small spines between them, covering the whole upper surface 
of the larva and the margins of its carapace. The greater part of these, or rather all, 
with the exception of some small hairs or hair-like spines, have openings at the top, and 
ducts from the glands, which densely fill the whole carapace, may be easily seen running 
up to them. 
The dorsal spine is movable, and a large muscle may be seen running into it. This 
has been represented in Plate 12, for which I have on purpose taken a specimen which 
was soon going to moult, and in which the muscles inside the large spines have grown 
so much that they cannot stretch out, but are obliged to coil themselves up. 
mdccclxxvi. u 
