26 COMPARATIVE ANATOMY. 



dividing the cephalo-thorax into a large anterior and a much 

 smaller posterior division, and bearing some resemblance to the 

 cephalic suture, to be subsequently described, in the lobster. In 

 the centre of the cephalo-thorax, and situated upon a little 

 eminence, is the medio-dorsal pair of 'oculi,' one on each side of 

 the median groove. There are also three additional 'oculi' at each 

 antero-external angle, on each side of the anterior median notch. 



The segmental appendages, of which there are six pairs, 

 namely, counting from before backwards, antennas, mandibles, 

 and four pairs of ambulatory legs, are entirely confined to the 

 c ephalo-thorax. Functional antennas are absent: but thehomo- 

 logues of the antennas of Insecta are the large and strong cheli- 

 form appendages situated in front of the mouth, and so modi- 

 fied from their ordinary structure as to become efficient 

 prehensile organs. The first post-oral pair, the mandibles, are 

 in this species remarkable for the extraordinarily dispropor- 

 tionate development of the mandible proper and its 'palpus.' 

 While the former is a small, internally flattened, slightly serrated 

 plate, the latter, absent in Insects and with the exception of a 

 rudiment, in Myriapods also, is enormously elongated, and carries 

 huge 'chelae' at its distal extremity. The two succeeding pairs of 

 appendages correspond to the two pairs of 'maxillae' in the lobster. 

 In the first pair the 'maxillae' themselves are small, somewhat 

 conical, curved inwards, and form the external lateral elements 

 of the ' labium.' The ' palpi,' on the contrary, are greatly elon- 

 gated, six-jointed appendages, with two small claws attached to 

 their distal segment. In the second pair a similar arrangement 

 exists. The maxillae are two triangular processes, applied by 

 their straight internal edges to each other in the median line, 

 and so forming the mesial elements of the ' labium.' The palpi 

 resemble those of the first pair of maxillae. The next two pairs 

 of feet, representing the two pairs of 'maxillipeds' in the 

 Lobster, and the two anterior pairs of legs in Insects, resemble 

 the maxillary palpi just described, with the exception that they 

 are longer, and have much larger basal segments. 



The next segment, which in the Crustacea would carry the 

 third pair of 'maxillipeds/ is, as in the Chilognathous Myriapods, 

 the genital segment. In the centre of the sternal surface of this 

 segment is the opening of the efferent duct of the reproductive 



