CRUSTACEA. 495 



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 Zoa^a. The hind 

 end of the shield is also produced into a long caudal spine (c.sp} 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 (lb] which covers the mouth 1 . At the sides 

 of the lip lie the three pairs of Nauplius appendages, which are very 

 characteristic but present no 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 appear- 

 ance 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 larvae 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 compound 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 maxillae and 

 internal to these a pair of small prominences, which are perhaps 



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

 upper lip, and 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 oesophagus. 



- The enormous spinous 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 Zoo?a. 



