ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 627 



fills the cavity and is only united to the wall by a narrow stalk. The 

 nematoblast gives rise to the thread ; the fluid which surrounds it 

 solidifies and forms the case of the nematocyst. When the thread is 

 barbed its development is more complicated ; in the interior of the 

 nematoblast a small sphere appears, this becomes hollow and invagi- 

 nated, and thus forms the barb. 



Stephanotrochus moseleyanus.* — Mr. W. L. Sclater describes a 

 new species of the genus Stephanotrochus, which is not only interest- 

 ing as being the finest and largest of the genus, but as the first 

 recorded from the British seas ; it was dredged by H.M.S. ' Triton' at 

 a depth of 570 fathoms in lat. 59° 51' N. and long. 8° 18' W. ; its nearest 

 allies were taken by the ' Challenger ' off the Azores and Pernambuco. 

 It differs from species already described by the greater development 

 of the pali, and the stouter primary and secondary septa, of which 

 there are altogether five complete cycles. The cord presents evidence 

 in favour of Koch's theory that the theca is formed from the fused 

 peripheral ends of the septa ; the darkly coloured oral disc, the 

 'tentacles, and outer soft wall contains polyperythrin ; the tentacles are 

 in four cycles, and those of the innermost are the largest and twelve in 

 nurnbsr. In the arrangement of the muscles on the mesenteries 

 Stephanotrochus exactly corresponds to the Hexactinian type, as do all 

 other madrepores that have yet been studied. The single specimen 

 examined contained ova only, so that the species is probably dioecious, 

 Cells, which appear to be calycoblasts, differ from those described by 

 Koch in having an irregular instead of a quadrangular shape ; this 

 may be due to their greater age. 



Polyparium ambulans.f — Dr. A. Korotneff describes from the straits 

 near the island of Billiton, a remarkable colony, 7 cm. long by 15 cm. 

 broad, which is bandlike in form, and on one side has the upper sharply 

 separated from the lower surface ; on the other side, however, they 

 pass into one another ; the anterior is not to be distinguished from the 

 hinder end. The upper surface is covered by peculiar polyps, the 

 base of each of which is much broader than the tip, which carries a 

 round orifice. The polyps appear to be altogether devoid of tentaole/i ; 

 They are not all of the same size, and the smallest, which have no 

 oral orifice, appear to be buds. 



The lower surface is covered with suckers, which are very regularly 

 arranged ; each row is set transversely, and is separated from its 

 neighbours by a transverse groove ; the suckers, like the polyps, vary 

 considerably in size ; the whole colony moves like Cristatella. 



The polyps have no septa, and the internal surface is quite smooth 

 and devoid of the ridges which might indicate an affinity with corals. 

 The lumen of each polyp passes into the spacious lumen of the foot 

 or body of the whole colony ; this is broken up by partitions into 

 divisions of equal size, but these partitions are certainly not the 

 homologues of the ordinary septa of polyps ; they are set transversely to 



* Proc. Zool. Soc, 1S86, pp. 12S-36 (3 pis.). 

 + Zool Anzrig., ix. (lS8t>) pp. 220-4. 



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