ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 045 



The larvas described differ in some particulars from those of 

 S. spirillum Gould, described by A. Agassiz, and even more widely 

 from the young of S. spirillum, described by Pagenstecher ; but are 

 considered by the author to be of the same species as that described 

 as S. spirillum by A. A. Gould. 



On escaping from the egg capsule, the young larva swims about 

 in the water with considerable activity, and is often captured with 

 the dip-net in surface fishing. The free larva often does not im- 

 mediately settle to the bottom prior to the secretion of the case in 

 which it lives, but passes through the preliminary stages while floating 

 on the water, until the increasing specific gravity of its body sinks it. 

 The case or shell is not at first coiled, but horn-shaped. The most 

 prominent structure about the body of the larva at this stage is an 

 oblong mass of cells of brick-red colour seen through the transparent 

 w^alls of the shell, but of their probable function nothing is said. 



Skin and Nervous System of Priapulus and Halicryptus.* — Dr. 

 R. Scharff finds in the skin of these Gcphyroa a third layer, or one 

 additional to the cuticle and hypodermis described by Ehlers ; this is 

 extremely thin, and consists of connective tissue ; it is well developed 

 in Sipunculus nudus, where it is the seat of secreting glands and of 

 accumulations of pigment ; the cuticle lines the interior of tho 

 oesophagus ; around the anus of P. caudatiis the hyi^odermis is 

 curiously modified, its cells being much elongated, and at the same 

 time expanded so as to form a compact mass, to which the author is 

 inclined to ascribe an excretory function. 



The proboscis of both Priap>ulus and Halicryptus is provided 

 with small dermal projections arranged in numerous longitudinal 

 rows ; on the body there are circular rows. In Priapulus caudatus 

 the spikes have the form of small trux!cated cones, just visible to the 

 naked eye ; through the circular opening at their top there project a 

 number of delicate hairs ; the spikes appear to be retractile. The 

 most striking analogy between these and sensory organs in other 

 animals is to be found by comparing them with the organs of the 

 lateral line in fishes. 



As to the nervous system, the author's results agree generally 

 with those of Horst ; in both genera examined the system lies entirely 

 in the ectoderm ; the position of the cord is marked externally by a 

 shallow groove on the ventral surface ; the apj^arent swellings seen at 

 regular distances along the nerve-cord seem to be due to the power- 

 ful contractions of the annular muscles, by means of which the cord 

 is found to bulge out in the intervening spaces. Dr. Scharff differs 

 from all his predecessors in stating that the nervous system lies not 

 immediately under the hypodermis, but within it. The ganglionic 

 are merely modified hypodermic cells. Unlike Sacnger, he was 

 unable to detect lateral nerves given off from the main trunk and 

 surrounding tho body as in Sijyunculus nudus ; though thiuking it 

 rash to deny tho presence of peripheral nerves, tho author inclines to 

 the view that the whole of tho hypodermis acts as a kind of nervous 



* Quart. Joum. Micr. Sci., xxv. (ISS.T pp. I9;5-213 (1 pi.). 

 Sf.r. 2.— Voj,. V. 2 U 



