A STUDY IN MORPHOLOGY. 85 



maxilliped (Mp. 3) is more like those which follow, but its hairs are shorter. The 

 first, second, and third pereiopods are about equal in length, and they have the typical 

 structure which has just been described ; but the endopodite of the fourth (Pr. 4), 

 like that of the second maxilliped, is shorter than the exopodite, although its hairs are 

 very long. 



At the last Schizopod stage (fig. 54) the series of limbs, shown from above in 

 fig. 59, is about as it is in the first stage, but the hairs on the endopodites of all the 

 appendages, except the last, are short. A comparison of one of these appendages 

 with the second antenna of the Nauplius or Protozoea or Zoea shows great similarity, 

 and I am therefore disposed to believe that the long jointed ramus of the antenna is 

 homologous with the long ramus of the thoracic limb, and consequently the 

 endopodite. 



The abdomen is very much longer in proportion to the carapace than it was at the 

 "Zoea" stage, and a comparison of figs. 50 and 54 with fig. 43 will show that it has 

 become flattened from side to side, while its vertical thickness has greatly increased. 

 All six somites are distinct, but at the first Schizopod stage there are no traces of any 

 abdominal feet except the swirnnierets, which are large and perfect. In the second 

 Schizopod stage the first five pairs of pleopods are represented by short buds, and in 

 the last Schizopod stage (fig. 54) they have nearly or quite their full size, but are still 

 rudimentary. 



The posterior edge of the ventral surface of each abdominal somite carries a couple 

 of spines (fig. 50) pointing backwards. They are small on all the somites except the 

 last, and they appear to correspond to those which, from their great size, have given the 

 name Acanthosoma to the larva of Seryestes at the same stage of development. The 

 sixth abdominal somite also has a small median dorsal spine. 



The telson (T) is movable, greatly elongated, three times as long as wide, and its 

 spines have become very small, although in number, arrangement, and relative size 

 they agree with those of the Zoea and Protozoea. 



The sixth pleopod or swimmeret consists of a short thick basal joint, a long flat 

 exopodite which is serrated along its inner edge and free extremity, but smooth 

 along its outer edge ; and a flat endopodite serrated on both sides. Each serration 

 carries a long slightly curved plumose hair, and the outer edge of the exopodite has a 

 small tooth at its outer end. From the base to the tooth the outer border is nearly 

 straight and parallel to the inner border, but the end of the appendage is prolonged 

 into a rounded tip which reaches beyond the tooth. In the first Schizopod stage there 

 are eight hairs on the inner border and four on the end of the exopodite, or twelve in 

 all ; and there are eight hairs on the endopodites, but the number of serrations and 

 hairs increases rapidly with each moult, on each division of the limb, and they are 

 much more numerous in the last Schizopod stage, as shown in fig. 54. 



A large reddish-brown pigment-spot (fig. 54, p) has now appeared on each side of 



WAT 



&/P 



/CO 





