1893.] and Functions of the Alimentary Canal o/Daphnia. 45 



region cannot be regarded as conclusive. The very small quantity 

 of fluid that is found at any time in the middle and posterior 

 regions of the midgut of a well-fed animal points to this con- 

 clusion. In the chlorophyll of the algae which form so large a 

 portion of the diet of Daphnias, we have a substance whose fate 

 we can to a certain extent trace, and we find that as digestion 

 proceeds the food mass in the middle region loses its green tint, 

 while the fluid contents of the anterior region become coloured 

 a vivid green. Further there is evidence that this dissolved 

 chlorophyll is absorbed, for the striated border of the epithelium 

 becomes coloured an intense green and the cells charge them- 

 selves with yellow pigment masses. 



Defcecation is a sudden act: the faeces, which are formed in 

 the posterior region of the mesenteron, are quickly expelled from 

 the intestine passing rapidly through the proctodseum. 



Defsecation is carried out by a wave of contraction which 

 appears to start at some undeterminable point in the mesenteron, 

 and a wave of dilatation and contraction passing backwards over 

 the proctodseum. The movements of the proctodseum are of such 

 a nature that they first aspirate the contents of the posterior 

 region of the mesenteron, and then expel them through the anus. 



There is undoubtedly a sphincter muscle at the junction of 

 mid and hind gut in Daphnia. 



The proctodseum also exhibits a rhythmical movement which 

 consists of peristaltic waves starting from the anus and travelling 

 forwards to the junction with the midgut. The interval between 

 successive waves varies (e.g. 3 to 9 seconds in one animal). They 

 have no connection with the forward running peristaltic waves 

 of the mesenteron, for the latter occur at quite regular intervals 

 without any reference to the time of occurrence of the procto- 

 deal wave. Thus in the case given above, the proctodeal waves 

 followed one another at irregular intervals varying from 3 to 

 9 seconds, while the peristalsis of the mesenteron occurred with 

 perfect regularity every 1| seconds. 



The rhythmic movements of the proctodseum appear to be 

 independent of the central nervous system, for they are main- 

 tained long after all signs of life have vanished and may be 

 shown by the proctodasum when isolated as completely as possible 

 in normal salt solution. They undoubtedly lead to the entrance 

 and exit of water and, in the absence of any definite knowledge 

 on the subject, we may perhaps regard them as respiratory in 

 character. 



It is clear that the stomodeal and proctodeal portions of the 

 intestine of Daphnia, so far as the manipulation of the food stuffs 

 is concerned, take part only in the processes of deglutition 

 and defsecation, and the ingesta and egesta are not lodged in 



