POLYCERA OCELLATA. 



These, with the difference in colour, constitute the chief distinctive characters, but there is 

 also observable some little difference in their habitats. On the Northumberland coast, where 

 it is not very rare, we have never found this species but within tide-marks ; P. Lessonii, on 

 the contrary, is generally found in deep water on the same coast, and is common upon 

 corallines brought in by the fishing boats ; but never, among the many specimens which we 

 have obtained by this means, have we found a single individual of P. ocellata. 



At Torquay we found this species in pools among the rocks near high- water mark. 



A curious light-coloured variety was brought to us among the produce of a day's 

 dredging in Dublin Bay, where it appeared to occur in tolerable abundance : we did not 

 learn at what depth, but from the other contents of the dredge we conclude that it was 

 in shallow water. This variety had the dark portion of the surface much reduced in size, 

 and forming little more than a network round the spots. Another variety occurs on the 

 Northumberland coast ; it is of a pale yellowish green entirely devoid of spots, and might 

 easily be confounded with the young of P. Lessonii, but for the tentacles and branchial 

 plumes, which are always sufficient to distinguish the species. 



The Triopa Notkus of Dr. Johnston is most likely the young of this species ; but, from 

 the imperfect state of the specimen from which it was described, it would be impossible to 

 speak with certainty. 



This animal floats frequently, and can fix itself by its tail with great firmness to any 

 substance over which it may be passing. It is sometimes difficult to detach it from the 

 polished surface of glass. Its heart beats from seventy-two to eighty-eight times in a 

 minute. Calcareous spicula are distributed through the skin, but are not crowded nor 

 placed in regular order. There are two kinds, one much larger than the other : the larger 

 is cylindrical, obtuse at the ends, a little bent in the centre and pretty regularly covered 

 with irregular circles of tubercular points ; the other kind is scarcely one third the size, 

 smooth, cylindrical, slightly bent in the centre and thickened and rounded at the ends. 



The spawn occurs in July and August — occasionally in September ; and is generally of 

 a delicate rose colour and of a strap form, attached by its edge to stones : it is usually two 

 or three times coiled, sometimes not so much, with the coils rather wide apart and angulated. 

 The eggs are of an oval form, and mostly in transverse rows. 



Fig. 1, 2, 3. Polycera ocellata, different views. 



4 A branchial plume, very highly magnified. 

 5, 6. Side and front views of a tentacle, much magnified. 



7. A portion of the skin, showing imbedded spicula. 

 8, 9. Spicula, more highly magnified. 



10. Spawn. 



11. A portion of the same more highly magnified. 



