THE PYCNOQONIDS. 3? 



plete metamorphosis, although I believe the set must be almost 

 filled out especially for the later stages. Here I could procure 

 great numbers of individuals, and, comparing them and finding 

 no intermediate stages, I inferred none such existed. But in the 

 very young stages, before the appearance of the first pair of 

 walking legs, it is extremely difficult to know how complete the 

 series is ; but from the slight gradations in size and structures in 

 those figured, I think we shall not be far wrong in assuming an 

 almost or entirely complete series. 



In Part I of the present paper I have figured and described 

 at length the structures of the Pantopod-larva of Tanystylum at 

 the time when it leaves the parent. I shall speak of an embryo 

 of this age as stage 1 (see Plate IY, Fig. IX). In examining the 

 hydroids for Sea-Spiders, I found one embryo a little larger in 

 size than this first stage, and having other slight differences which 

 plainly show it to be a stage in advance of the last, and probably 

 a stage immediately following stage 1, or after the first larval 

 skin is shed. Figures of this stage (2) are seen in X and XI of 

 Plate Y, showing the ventral and dorsal views respectively. 

 The embryo has much the same shape as stage 1, but there is 

 seen an important difference between the two stages. The older 

 larva has the posterior part of its body filled with a solid lobed 

 mass of cells, which contrasts strongly with the clear posterior part 

 of stage 1. Further, the second pair (really the third, as the first 

 is double) of ventral ganglia are much larger. The posterior 

 pair of lobes of the mid-gut project to the sides of the embryo, 

 and an examination of the periphery of the posterior border 

 shows a slight indentation on each side, indicating the beginning 

 of another pair of appendages. The first pair of appendages, 

 the mandibles, are three-jointed, and have, projecting forward 

 from the first, proximal joint, a strong spine, as in stage 1. The 

 second and third appendages are each two-jointed, with a strong 

 terminal, movable spine. The proboscis lies in the mid-ventral 

 line, and projects forward between and ventral to the first pair 

 of appendages. Fig. XI shows the dorsal view of the same 

 embryo. From the figure we see that the digestive tract of the 

 embryo is on each side three-lobed. The first pair of lobes pro- 

 jects into the first pair of appendages, the second pair of pouches 

 towards the base of the third pair of appendages, and the third 



