103 



the reason of the dying of the algae is especially of theoretical 

 interest and not so much of practical, as indeed all dead algae 

 come to the benefit of the nourishment of the sponge. 



It is rather a complicate question, which I am going to treat 

 more in extenso. 



«F 



I. In the first place we will answer the question, what causes 

 are theoretically possible for the dying of the green algae in the 

 amoebocytes, and at the same time if those causes should have 

 to behave differently in a sponge in light and in a sponge in 

 darkness : 1st Of course : the spor^ge cells might actively kill the 

 algae with the aim to digest them, so from want of food. Would 

 there be any reason then to accept, that this cause would be 

 active in light in another degree than in darkness? Certainly! 

 One might expect, that the amoebocytes of a sponge in darkness 

 should kill the algae in a higher degree than those of a green 

 sponge in light. For some pages back (p. 97 — -98) we had several 

 sound reasons for supposing, that a sponge in darkness would 

 need more food than a green one in light. The more so, as we 

 saw on p. 100, that the sponges are very likely to transform 

 relatively great quantities of energy in the flagellar-motion of 

 their choanocytes, in which transformation iu case of lack of O,^ 

 not only more N-free materials, but very likely also the proteins 

 themselves of the choanocytes are broken down and, consequently, 

 must be restituted (p. 98). As 2nd cause of the dying of the 

 green algae in the sponge cells comes into consideration: „poi- 

 soning" — so to say — of the algae by products of metabolism 

 of the sponge, so without any relation to the want of food and 

 the nourishment-process but, for instance, more as a reaction of 

 defence of the sponge against a foreign intruder. There is no 

 certain proof for this possibility, but some indication in the 

 direction of poisoning of the algae by products of metabolism 

 can be the behaviour of isolated green sponge-algae, when there 

 appears in their culture a strong infection of diatoms, mould, or 

 ordinary ■ green algae. For, as I have mentioned already on p. 43 and 

 45, the sponge algae die under such circumstances. (On the other 

 hand the cultures 



