16 Prof. J. C. Schiodte on the Structure of 



In front the oral tube is closed by the lahrum^ which hangs 

 perpendicularly from the clypeus ; this latter is itself in a 

 perpendicular position, elongated and arched in front. The 

 labrum is of semicircular outline, and edged by a thick, soft, 

 membranaceous fringe, which is dotted over with small pointed 

 warts. 



When the maxillipeds are removed, we observe the short 

 prosternum, and in front of it the sphenoid plate, on which 

 an elevated ridge is conspicuous along its middle line, which 

 becomes gradually thinner towards the apex, besides the sockets 

 of the cardo and stem of the maxillipeds, and, finally, the 

 second pair of maxillce. As we have stated already, a depres- 

 sion is observed on either side between the latter and the 

 middle ridge of the sphenoid plate, which is filled up by the 

 longitudinal crest on the upper surface of the stems of the 

 maxillipeds. The consequence is that the stems of the second 

 pair of maxillae are entirely covered in from beneath by the 

 stems and the base of the palpi of the maxillipeds. The 

 stems of the second pair of maxillas present the shape of elon- 

 gated, inverted-pyriform, thin and uneven saucers, somewhat 

 narrowed and flattened towards their fore ends, which meet across 

 the middle ridge of the sphenoid plate, just inside and above 

 the second joint of the palpi of the maxillipeds. Their con- 

 cavity is, of course, turned upwards towards the under surface 

 of the skull ; and in the sjjace thus enclosed the maxillae of the 

 first pair are lodged, with sufficient spare room to insure their 

 free movement. The maxillary lobes of the second pair are 

 small, thin, of rounded outline, at the apex and along the 

 inner margin armed with some small, rather soft, hooked 

 spines. The rounded outline of the lobes, however, only ap- 

 pears when they are unfolded ; for in their natural position 

 their appearance is very different. The inner lobe is then 

 observed (j:;*, fig. 4 h) in the slit between the palpi of the 

 maxillipeds, at the inner posterior corner of the second joint ; 

 but it is twisted round, so that it is seen foreshortened, and 

 the hooks above mentioned seem in consequence to form al- 

 together but one thick thorn. The whole anterior margin of 

 the outer lobe, on the contrary, is turned back like a collar over 

 the anterior margin of the second joint of the maxillipeds. 

 The part played by the second j)air of maxillae in the con- 

 struction of the sucking-apparatus is consequently this, that 

 their stems are excavated into sheaths for the stylifonn first 

 pair of maxillae, and their lobes fill up the remaining gaps 

 in the sucking-tube, of which the opening becomes a closed 

 circle formed by different elements which can slide over each 

 other and are armed with small hooks. 



