Mr. J. S. Bowerbank on the Cocoon of a Leech. 301 



XLII. — On the Structure of the Cocoon of a Leech. By J. S. 

 BOWKRIJAXK, F.K.S., L.S. &c. 



[Willi a Plati'.] 



At the first view, I believed that the very curious body which is 

 the subject of the ])resent communication was one of the singular 

 aberrant forms of that exceedingly variable tribe the Spon(jiada, 

 and until I received a note from Professor Henslow, kindly in- 

 timating the probability that I had fallen into an error in thus 

 designating it, I entertained not the slightest doubt of its being 

 one of the numerous odd forms that abound among the sponge 

 tribe, and especially so from the remarkably abundant and de- 

 ceptive sponge-like tissue with which the body of the cocoon is 

 enveloped. 



The distinct coriaceous body with its mannnillatcd terminations, 

 so unlike the great mass of the Sponyiadce, woidd naturally have 

 made it the type of a new genus, and as sucli I had described it. 

 I am therefore the more anxious that this error should be repaired 

 as completely as possible, and to prevent the chance of its recur- 

 rence, I have thought it advisable to describe the stracture and 

 peculiarities of this cm'ious little body, although other cocoons 

 somewhat similar have already been to a certain extent made 

 known to the scientific world through the works of Dr. James 

 Rawlins Johnson on the Medical Leech, and of Dr. Noble. The first 

 of Dr. Johnson^s memoirs was published in the year 1816, and 

 the second in 1825, and that of Dr. Noble in the year 1822. In 

 the latter treatise of Dr. Johnson we have engravings of the co- 

 coon of the medicinal leech from drawings by i\lr. Clift, and also 

 from a cocoon sent to the author by Dr. Noble ; and in a subse- 

 quent portion of the work we have the cocoons of Hirudo vulgaris 

 figured and described ; but in neither of these can we recognise 

 the distinct and singular sponge-like fibrous envelopment of the 

 species I am about to describe, and the cocoon of the latter spe- 

 cies especially appears from the figures to be completely destitute 

 of any such appendage. It is therefore probable that the subject 

 of the present memoir is the cocoon of Hirudo sanguisuga, the 

 common horse leech, an animal which differs very considerably 

 both in structui'e and habit from the before-named species ; or it 

 is a species, the cocoon of which has not hitherto been described. 



Dr. Noble designates the cocoon which was the subject of his 

 observations as being of the size and figure of that of the silk- 

 worm, and as having the same appearance and density as a piece 

 of fine sponge, but although the description in the latter respect 

 agrees with the one I have to describe, the figure of it in Dr. John- 

 son's work is evidently that of a different species. 



