CRUSTACEA. 411 



The dorsal shield of the Nauplius of Lepas fascicularis (fig. 231) becomes 

 somewhat hexagonal, and there springs from the middle of the dorsal 

 surface an enormously long spine (d.sp), like the dorsal spine of a Zoaea. 

 The hind end of the shield is also produced into a long caudal spine (c.sj)) 

 between which and the dorsal spine are some feather-like processes. From 

 its edge there spring in addition to the primitive frontal horns three main 

 pairs of horns, one pair anterior, one lateral, and one posterior, and smaller 

 ones in addition. All these processes (with the exception of the dorsal 

 and posterior spines) are hollow and open at their extremities, and like 

 the primitive frontal horns contain the ducts of glands situated under 

 the shield. On the under surface of the larva is situated the unpaired 

 eye (oc) on each side of which spring the two-jointed frontal sense organs. 

 Immediately behind these is the enormous upper lip (Ib) which covers 

 the mouth 1 . At the sides of the lip lie the three pairs of Nauplius ap- 

 pendages, which are very characteristic but present 110 special peculiarities. 

 Posteriorly the body is produced into a long ventral spine-like process ( Vp) 

 homologous with that of other more normal Nauplii. At the base of this 

 process large moveable paired spines appear at successive moults, six pairs 

 being eventually formed. These spines give to the region in which they 

 are situated a segmented appearance, and perhaps similar structures have 

 given rise to the appearance of segmentation in Spence Bate's figures. 

 The anus is situated on the dorsal side of this ventral process, and between 

 it and the caudal spine of the shield above. The fact that the anus 

 occupies this position appears to indicate that the ventral process is 

 homologous with the caudal fork of the Copepoda, on the dorsal side of 

 which the anus so often opens 2 . 



From the Nauplius condition the larva?, pass at a single 

 moult into an entirely different condition known as the Cypris 

 stage. In preparation for this condition there appear, during the last 

 Nauplius moults, the rudiments of several fresh organs, which are 

 more or less developed in different types. In the first place a com- 

 pound eye is formed on each side of the median eye. Secondly there 

 appears behind the mandibles a fourth pair of appendages the first 

 pair of maxilla? and internal to these a pair of small prominences, 

 which are perhaps equivalent to the second pair of maxillae, and give 

 rise to the third pair of jaws in the adult (sometimes spoken of as the 

 lower lip). 



Behind these appendages there are moreover formed the rudi- 

 ments of six pairs of feet. Under the cuticle of the first pair of 

 antennae there may be seen just before the final moult the four- 

 jointed antennae of the Cypris stage with the rudiment of a disc on 

 the second joint by which the larva? eventually become attached. 



1 Willemoes Suhm (No. 530) states that the mouth is situated at the free end of 

 the upper lip, aud that the oesophagus passes through it. From an examination of 

 some specimens of this Nauplius, for which I am indebted to Moseley, I am inclined to 

 think that this is a mistake, and that a groove on the surface of the upper lip has 

 been taken by Suhm for the ossophagus. 



2 The enormous spiuous development of the larva of Lepas fascicularis is probably 

 to be explained as a secondary protective adaptation, and has no genetic connection 

 with the somewhat similar spinous armature of the Zosea. 



