KNOWLEDGE OF THE CHOANOFLAGELLATA. 21 



Sometimes an apparent desire for exercise, especially after 

 division, leads the animal to leave its station and swim about in 

 the water. It is interesting that the method of progression is 

 then with the flagellum hindmost, whereas in most free-swimming 

 flagellates the flagellum is foremost. The collar is contractile, 

 and at certain times retractile. The nucleus lies in the body 

 near the base of the flagellum, and is generally visible as a 

 rather dense sphere surrounded by a clear area. One or two 

 contractile vacuoles are present at the end of the body furthest 

 from the flagellum, and may be seen to pulsate more or less 

 regularly. Several food vacuoles containing solid particles render 

 evident by their movements a circulation or streaming of the 

 body protoplasm. 



The method of nutrition is undoubtedly by the ingestion of 

 solid particles, bacteria, etc., but where and how these particles 

 are taken into the body are disputed points. Saville Kent 

 described them as passing up the outside and down the inside of 

 the collar, to be absorbed by the body protoplasm near the base 

 of the flagellum. He stated that the movement was brought 

 about by a circulation in the hyaline protoplasm of the collar, 

 which he was able to observe by the use of exceptionally high- 

 power objectives. No one of the other workers on these forms has 

 seen this circulation, and to any one who has observed the collar 

 through a yV" objective, Saville Kent's description sounds won- 

 derful indeed. Even with the best illumination and using 

 eyepieces x 12 or x 18, the collar can rarely be seen as other 

 than two lines, one on either side of the flagellum. For this reason, 

 Biitschli and Fisch both depict the collar thus, although recog- 

 nising that it is really a collar-like membrane. Vacuoles can 

 be seen protruding from the general outline of the body at the 

 base of the collar ; according to both Biitschli and Fisch the food 

 particles are absorbed into the body outside the collar, according 

 to Saville Kent inside the collar. Entz and France hold a middle 

 course, and describe the collar as a spirally wound membrane down 



