KNOWLEDGE OF THE CHOANOFLAGELLATA. 23 



flagellate and the choanocytes of sponges, but our knowledge of 

 the development of sponges, largely due to the work of Professor 

 Minchin, shows that the relationship between Choanoflagellata 

 and Porifera, if any, must be very remote. Diplosiga is a 

 form found by Frenzel, possessing two collars. All the above- 

 mentioned forms are without any protective covering, but the 

 following forms secrete a case or lorica in which the animal lives. 



Salpingoeca (Plate I., Figs. 3 and 4) is the genus most rich 

 in species, about thirty-two having been described. Probably, 

 however, some of these are varieties or growth forms ; and France, 

 in his monograph, contents himself with describing five types of 

 Salphigoeca. Polyoeca (Plate I., Fig. 5) is a colonial Salpingoeca 

 seen by Saville Kent in 1874, but appears to be of rare 

 occurrence, for neither France nor the other workers in this 

 group seem to have seen it. The author was fortunate enough, 

 however, to find a new species of this genus fairly plentiful in 

 a tank at the Plymouth Biological Station. JDijylosigopsis is a 

 form found by France, with two collars and a lorica, corresponding 

 to the non-loricate form Dij)losiga. These double-collared forms 

 are puzzling, and from France's drawings of Diplosigopsis one 

 is tempted to suggest that the second collar may be really the 

 neck of the lorica in a Salpingoeca, If such forms do exist, 

 however, they should not be classed with single -collared forms 

 as France classes them, and certainly, too, they would rather 

 tend to weaken Entz's theory of the spiral structure of the 

 collar, unless the animal were the happy possessor of two 

 mouths. 



The affinities of the Choanoflagellata are quite obscure. 

 France thought that Bicosoeca, a flagellate living in a lorica, and 

 with a peculiar membrane at the base of the flagellum, might 

 be related to Salpingoeca ; but in many respects ^^cosoec appears 

 to be rather specialised. In Phalansteriuyn we find a membrane 

 encircling the base of the flagellum, resembling, but not identical 

 with, the collar of Choanoflagellates. But Phalansterium does 



