412 RECORD OF CURRENT RESEARCHES RELATING TO 



Changes in Form, Movements, «S:c.* — Dr. Krukenberg points out 

 tliat cliauges in form, movements, &c., may take place in various 

 ways : 



(1) By the direct influence of external forces : 



(a) Change in the form of the surface of the body (Me- 

 dusfe). 



(h) Protoplasm being influenced by light, heat, or gravi- 

 tation (heliotropism and geotropism of various 

 plants). 



(c) Change in specific gravity (Ctenophora). 



(d) When the specific weight is greater than that of the 



surrounding medium (birds in air). 



(2) By the elasticity of organized bodies, and parts secreted by 



an organism (joints of various animals). 



(3) By the retention of fluids in cavernous structures : 



(a) Pure blood is retained in the pecten of the fowl. 



(b) Blood and water erect the anal appendage in Porina. 



(c) Water with some organized constituents erects the 



ambulacral feet in the Asterida. 



(d) Almost pure water fills the tentacles of the Actiniaj. 



(4) By the attraction of water : 



(a) In protoj)lasm (leaf-stalks of Mimosa pudica). 



(b) In extensile substances (mantle of Botryllus). 



(5) Without any evident loss of water : 



(a) Amoeboid protoplasm (wandering cells). 



(6) Contractile tissues of definite structure (muscles). 



B. INVERTEBRATA. 



Process of Digestion in the Invertebrata.-j- — Dr. Krukenberg 

 discusses this subject ; commencing with some general considerations 

 on the various modes of nutrition exhibited in living forms, he points 

 out that they may be thus grouped : — 



(1) Nutrition is effected merely by absorption and assimilation; or 



(2) Digestive processes are added on. 

 Digestion itself may be effected — 



(i.) By means of enzymatous secretions in the contents ; 

 (ii.) Intracellularly, by enzymatous substances ; 

 (iii.) Intracellularly, by morphological ferments. 



(3) Mechanical arrangements may aid in the absorption of food ; or 



(4) Digestive processes and mechanical ai-rangements may combine 

 with the processes of absorption and assimilation to efiect nutrition. 



The mode of nutrition is not necessarily connected with the 

 arrangement of cells into tissues and organs ; firm bodies may be- 

 come flowed around by cytods, and intracellular digestion may 

 thus be efiected. Where, in the Invertebrata, digestion is efiected 

 by means of enzymatous digestive secretions, the author states 

 that he has always been able to find them in the tract during the 



* ' Vergl.-Physiol. Stud. Kiist. Adria ' (Krukenberg), i. (1880) p. 1. 

 t Ibid., (1879) p. 38. 



