ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 49 



latter, from eight to twenty- two being there developed ; but in their 

 case the intersegmental grooves are not found at the sides of the 

 body ; they are all provided with a single lateral row of setae. The 

 hindermost part of the body is characterized by the presence of a 

 ventral shield which on the ventral surface takes the place of a number 

 of segments. The gill-filaments are spirally coiled and form two 

 dorsal pre-anal tufts. On examining the dermo-muscular tube it is 

 found that the hypodermis in the median segments forms a homo- 

 geneous layer, here and there traversed by fine fibres of connective 

 tissue, but altogether devoid of the unicellular glands which are so 

 frequently found in this layer in Chsetopods and other Gephyreans ; 

 the structure of the hypodermis in other regions is also described. 

 The cuticle is much thicker at the posterior than at the anterior end 

 of the body and is thicker than in any other Gephyrean or Chaetojjod 

 known to the author. The cross-bands found on it seem to prove that 

 in life the cuticle must be intensely iridescent. The surface of the 

 cuticle is covered with special dermal cirri, which are continuous with 

 the subjacent layer by dermal pores ; these cirri are filamentous and 

 vary in form in different parts of the body ; capillaries have been 

 observed in some of them, and there seems to be no doubt but that 

 they have a respiratory function. 



Sternaspis is distinguished from all other Gephyrea and Polychseta 

 by the peculiar disposition of its setas, which fall into three different 

 groups, the arrangement, muscular supply, and development of which 

 are fully described. 



The cerebral ganglia occupy the whole of the cephalic lobes ; the 

 ganglion- cells occupy the upper, lateral, and basal parts, while the 

 fibrous substance lies between them ; there is still a close connection 

 with the ectoderm. The greater part of the brain consists of cellular 

 elements, which exhibit distinct bilateral symmetry; the cells vary 

 greatly in form and size. The two bands of the oesophageal ring are 

 proportionately long, and consist of fine nerve-fibres, without any 

 ganglion-cells. The ventral cord is regularly rounded, and at first 

 lies freely in the coelom ; it then runs between two bands of longi- 

 tudinal muscles, without giving rise to any ganglionic swelliugs till 

 the end of the body is reached ; the complicated arrangement of the 

 cells and fibres in the cord was made out by the aid of sections. 

 Comparing this system with that of allied forms the author finds it to 

 be intermediate between what is found in Gephyrea and Chgetopods. 

 On the other hand, in the character of the enteric canal Sternaspis 

 stands nearer the Gephyrea than the Chsetopods. 



The vascular system is very complicated ; in addition to the two 

 primary vessels, or hearts, there are a number of lateral vessels, which 

 form remarkably close plexuses in all the organs, and there is also a 

 special branchial system. There appear to be a pair of lateral vessels 

 for each segment of the body. The segmental organs form a pair of 

 brown bodies lying on either side of the oesophagus in the fifth and 

 sixth segments ; they are of a spongy texture and may be seen to contain 

 a quantity of refractive concretions, which prove their renal function ; 

 they have no external orifices. The sexes can only be distinguished 



Ser. 2.— Vol. II. E 



