THE POSITION OF SPONGES, ETC. 429 



contribution to the subject was undoubtedly the discovery 

 of a peculiar form of colonial Choanoflagellates, to which he 

 gave the name Protospongia, afterwards corrected by him 

 in his description of the plates to Pi^otcrospoiigia, the 

 former name being preoccupied. The interest of this form 

 lies in the fact that it consists for the most part of a 

 structureless jelly in which zooids of different kinds are 

 imbedded ; at the exterior are typical Choanoflagellate 

 zooids, which serve for the nutrition and locomotion of the 

 colony ; in the interior are found amoeboid zooids, which 

 arise by modification and immigration of the Choanoflagel- 

 late zooids, and which multiply by binary fission dividing 

 up to form spore masses. Each spore becomes a " simple 

 minute uniflagellate monad " which travels to the surface of 

 the colony and is set free. There is thus formed in the 

 interior of Proterospongia a tissue very like the gelatinous 

 parenchyma of sponges, especially of those without a skele- 

 ton. 



From Proterospongia it is easy to understand Kent's 

 idea of the nature of sponges. He regards, in fact, a sponge 

 as consisting also of collar-bearing monads, imbedded in a 

 jelly containing amoeboid cells, the latter derived by modi- 

 fication of the collar cells. Those aniceboid cells may 

 secrete a skeleton, which is, however, not essential. As in 

 Proterospongia, so in sponges, Kent professed to have 

 discovered a sporular method of reproduction of the zooids. 



Collar cells according to him {p. 174) retract their 

 flagella and collars, "assume a quiescent or encysted 

 state," and "become resolved into the spore masses". 

 " The sponge body is, by ever-progressing internal spore 

 production, rapidly increased in size" (p. 176). These 

 statements of Kent are not supported by the testimony of 

 any other observer, and it is extremely probable, as Schulze 

 remarks (1885, p. 186), that Kent has mistaken bodies of 

 various kinds, such as spermatozoa, pigment granules, cells 

 containing reserve material, etc., for spore masses. Kent 

 denies the existence of spermatozoa and sexual reproduction 

 altogether in sponges. The supposed ova, according to 

 him (p. 187), are simply retromorphosed collar cells, which 



