14 HIRUDO. 



I was afterwards gratified to find that it had come under the notice 

 of Dr George Johnston, who, considering it a leech, had named it 

 UdoneUa ccdigorum. 



This is a minute white cylindrical animal, with a sucker at the 

 posterior extremity, whereon it rises erect, or swings the body in all dif- 

 ferent positions. The integument is too opaque to expose the contents 

 distinctly. None of my specimens extended to more than two lines, those 

 of Dr Johnston have equalled four, nor have they been alike opaque. 



This animal is not always present on the Caligus, but it sometimes 

 appears in great numbers. By gross enumeration about 150 were com- 

 puted as adhering to a dead Caliyus. 



There are frequently present along with specimens on the Caligus 

 numerous clusters of extremely minute capsules, as they appear ; some 

 full, and others of the same cluster empty. But whether these belong 

 to the Udonclla is uncertain. 



Extremely minute specimens of the Udonclla are occasionally seen 

 on the neck of the Hirudo muricata, lurking among the prominences. 



Though a longer series of observations, conducted under favourable 

 circumstances, might be requisite to determine the precise position of the 

 Udonella caUgorum, it may safely receive a provisional place among the 

 Hirudines. 



6. HIRUDO OCTO-OCULATA, SEU VULGAKIS. The Eight-eyed Leech. 



Plate II. 



I have not ascertained that more than four marine leeches, including 



* O 



the H. grossa and Udonella, belong to Scotland. But those inhabiting the 

 fresh-water are perhaps more than in due proportion to the space which 

 the whole territory occupies on the surface of the globe. If the number 

 specified here have fallen under the notice of one individual, it may be 

 readily presumed that more have occurred to others. I consider it for- 

 tunate when we can study the genera of animals without having re- 

 course to those of foreign seas. If the matter be viewed philosophically, 



