V. 



Parasites on Algae. 



LIKE most other subjects that take their turn in popularity as 

 fields of research, this one is by no means so new as may 

 readily be thought. There are few things in Nature that our " rude 

 forefathers," with their ruder appliances, did not grapple with after 

 some fashion. The earliest mention of any fact that may be classed 

 under this heading is probably the discovery of the so-called " galls" 

 in the well-known siphoneous Alga Vaucheria. They were described 

 and figured by Vaucher (i) so long ago as 1803, and many observers 

 since then have added to the list of species infested, and have 

 described the parasites and their operations. Of these writers, 

 Balbiani (2) has given the most exhaustive account. The parasite 

 in this case is an animal, and is described in the earlier papers as 

 Cyclops lupula, but Balbiani and others refer it more accurately to 

 Notommata werneckii. In a paper on the subject by Professor Oliver 

 (3), the animal is given on the authority of the late Mr. Gosse as pro- 

 bably Rotifer vulgaris. The parasite enters a lateral fertile branch at 

 an early stage, and sets up hypertrophy, causing it to swell to four or 

 five times its original size. These galls have been frequently observed, 

 as has been said, and an extensive literature has arisen on the subject, 

 which will be found fully cited by Mr. A. W. Bennett (4), who gives 

 from Benko the following list of species on which they have been 

 observed i—F. racemosa, dichoioina, davata, caespitusa, geminata, uncinata, 

 and terrestyis. Lister observed them on V. avevsa and V . dillniyni. 



It is extremely probable that a considerable number of animals 

 make use of Algae as their hosts, as they do of land plants ; but 

 botanical literature, so far as I can discover, contains remarkably 

 little about it. Miss Barton (5) has described malformations of the 

 thallus of the common dulse, Rhodyiucnia palmata, caused by a copepod, 

 Havpacticns chelifev, which inhabits the tissues and burrows in them 

 during a stage of its existence. The same enthusiastic phycologist (6) 

 has recently described two other similar cases, viz., gall-like structures 

 on Desmavestia aculeata, also caused by a copepod (too immature for 

 determination), and very remarkable malformations of Ascophylhim 

 nodosum, caused by a nematode worm, Tylenchus fncicola. This worm, 

 nearly related to the well-known " '.vheat-eels," has been minutely 

 described and beautifully figured by Dr. de Man (7). 



