514 Mr. II. M. Beinara on the 



But confining our attention solely to the forms which we 

 assume persisted in their more active free-swimming habits, 

 a vista of possibilities opens out with regard to them which 

 seems to lead straight to the typical Annelid. 



It appears at first sight as if there would be no limit to the 

 possible addition of fresh buds, so that, excluding accidents, 

 each original (or parent) animal would soon trail after it a 

 string of buds of indefinite length. Mechanical difficulties, 

 however, would most certainly sooner or later arise. Tiie 

 most important difficulty would, it seems to me, be the 

 following : — The first-formed buds would have considerable 

 difficulty in getting rid of the indigestible remains of their 

 food. The parent animal, or first segment, was probably able 

 to get rid of faecal remains through the mouth ; but this would 

 be very difficult for the buds, and, indeed, progressively 

 difficult the further back they were. The aperture leading 

 from sac to sac we may justl}' presimie to have been, at least 

 primitively, very small, and it may perhaps have remained so 

 in the immediate ancestors of the segmented Worms. Before 

 long, therefore, particles of faecal matter would be mixed with 

 the food which found its way back into the last-formed bud, 

 until in time the faecal matter from the progressively increasing 

 number of digesting buds would make the arrival of food- 

 particles from the mouth impossible. Some nutriment might 

 for a while be extracted from this faecal matter, but the poste- 

 rior segments would eventually be so poorly nourished that 

 further budding would cease. This difficulty was hardly 

 likely to last long. Apertures can occur almost anywhere in 

 the Coelenterate wall, as we know from the apertures in the 

 walls of the Sea-anemones for the discharge of acontia. 

 Hence a posterior opening might early be developed in order 

 to free the terminal buds from their useless and deleterious 

 burden *. The muscular fibres of the walls would provide the 



said for it. The tentacles of Temnocephahi may be secondary adaptations 

 to its sessile manner of Hfe ; but the fact discovered by Professor tiaswell 

 (Quart. Jouru. Micr. Sci. xxviii., 1888), that the young of the Australian 

 forms invariably have six, while the adult has only tive tentacles, is signi- 

 ficant latlier of the opposite view. ]My esteemed friend and teacher 

 Prof. Arnold Lang (Text-book of Comp. Anat. pt. i.) al<o suggests an 

 origin from free-swimming Ccelenterates which have secondarily adopted 

 a creeping manner of life, but along an entirely diilerent line, viz. through 

 the Ctenophora, certain specialized forms of which furnishing almost ideal 

 intermediates. 



* Cf. Prof. Sedgwick's account (/. c.) of the possible origin of nephri- 

 dial apertures out of the constricted gastric pouches, which, according to 

 bis theory, gave rise to the ccelomic chambers. 



