A STUDY IN MORPHOLOGY. 79 



During the first Protozoiu stage (Plate 3, figs. 28 and 29) it lias only one denticle, 

 which is large and pointed, and situated at the posterior angle of the cutting edge ; Imt 

 at the second Protozoea stage (Plate 4, fig. 37) a number of smaller denticles have 

 appeared in front of the long one. The mandibles are never quite symmetrical, but 

 the outline of the left always differs a little from that of the right. 



The external surface of the first maxilla of the first Protozoea is shown in fig. 30, 

 and the posterior surface of that of the second Protozoea in Plate 4, fig. 38. It 

 consists, at both stages, of a basal portion made up of two joints with cutting hairs 

 (fig. 38, i and 2) ; a two-jointed endopodite (en), with three long slender hairs ; and an 

 exopodite or scaphognathite (figs. 30 and 38 sc), with three long slender hairs. In 

 the first stage (fig. 30) the hairs of the scaphognathite are simple, but in the second 

 stage (fig. 38) they are plumose. 



The posterior surface of the second maxilla of the first Protozoea is shown in Plate 

 3, fig. 31, and that of the second Protozoea in Plate 4, fig. 39. It consists of a 

 many-jointed basal portion (b), a two-jointed endopodite (en), and a scaphognathite or 

 exopodite (sc). The whole inner edge of the appendage carries short stout hairs ; the 

 tip of the endopodite a few somewhat longer hairs ; and the scaphognathite three 

 slender plumose hairs, which are much longer in the second than in the first stage. 



The first maxilliped (figs. 32 and 40) is very similar to the second antenna, and 

 consists of a two-jointed basal portion, a four-jointed endopodite, and an unjointed 

 exopodite. The inner edge is set with short stout hairs, which are simple in the 

 first, but irregularly plumose in the second Protozoea stage. The terminal joint of the 

 endopodite" carries four long slender simple hairs, and the tip of the exopodite four 

 long straight slender hairs, which are plain in the first but regularly plumose in the 

 second stage. 



The second maxilliped of the first Protozoea is shown in fig. 33, and that of the 

 second Protozoea in fig. 41. It is essentially like the first maxilliped in structure, but 

 much smaller, and apparently of little functional importance. 



In the second stage there is a small convoluted shell gland (fig. 35, sg), which 

 appears to open at the base of the first maxilla ; but the constant and violent 

 movements of the limbs render it difficult to decide with confidence exactly what its 

 relation to them is, and it is possible that its opening is upon the base of the second 

 instead of first maxilla. 



In the second Protozoea stage the two pigment-spots (/>) on the carapace become 

 extremely dendritic, and a pair of a,nal pigment-spots (Plate 3, fig. 34, pj>) make 

 their appearance on the telson on each side of the anus. 



At this stage the area, when the oesophageal muscles are attached to the carapace, 

 is somewhat peculiarly marked by six little circles arranged in a pentagon, as shown, 

 highly magnified, in fig. 35o. 



