Marine Worms as Microscopical Objects. By H. C. Sorby. 3 



Nearer the tail-end are many small vessels, and the enlargement and 

 contraction of the longitudinal vessels gives rise to a sort of spotted 

 appearance. In my mounted specimens the vessels in all parts are 

 very perfectly defined, and the blood of a brilliant red colour, without 

 any indication of decomposition or fading. 



Nephthys. — This shows well the larger vessels passing from the 

 centre to the surface in each ring, and numerous smaller ones between 

 them. There is but little difference from one end to the other, 

 except in the amount of vessels, and that near tie head -end there 

 are numerous oblique ones. The longitudinal vessels are best seen 

 towards the tail-end. Though well preserved in some parts, and the 

 blood bright red, the vessels are much less perfect in others, decom- 

 position evidently occurring much more readily than in Cirratulus. 



Nereis. — My specimen shows a single or divided large longitudinal 

 more or less lobed vessel, and sundry large transverse vessels in each 

 ring, with smaller ones between them, especially over the intestine 

 and in the pseudopodia, in which they form a beautiful network. The 

 chief difference in different parts of the body is that the longitudinal 

 vessel is much more simple in the anterior than in the posterior part, 

 where it is enlarged and contracted, and twisted about to a remarkable 

 extent. The blood is of a fine red colour, and the large and small 

 vessels are well preserved in some parts, showing the minute capil- 

 laries to great advantage ; but the red colour and the vessels are 

 completely lost where decomposition has occurred, probably owing to 

 injury in collecting. 



Sabella.— Compared with the genera already described, the de- 

 velopment of the blood-vessels is so much less that, when living or 

 recently dead, the blood does not attract attention by its red colour. 

 The character of the vessels also differs greatly, and is very different 

 in different parts of the body. In some places the main longitudinal 

 vessel is well seen, sending the larger lateral branches into each seg- 

 ment, with smaller vessels between them, especially over the intestine. 

 In other parts, this main vessel is represented by a curious develop- 

 ment of zig-zag vessels, either of comparatively simple character, or 

 assuming complicated tree-like forms quite unlike anything seen in the 

 other genera. The salt is so difficult to remove that all my specimens 

 show crystals. The blood is now more brown than red. The minute 

 capillaries are well seen in some places, but were either poorly 

 developed originally, or have been lost, though not by general decom- 

 position. The glycerin method is evidently only so far satisfactory 

 in this genus as to show how much its structure differs from that of 

 the other genera, and to indicate to some extent why the method so 

 completely fails with such forms as Arenicola and Terebella. 



Taking then all into consideration, the difference between the 

 different genera is very striking, though in the arrangement of the 

 blood-vessels Nephthys and Nereis are much the most closely related, 

 and Cirratulus and Sabella the most distinct. 



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