ENCYSTMENT OF TARDIGRADA. 845 



absent, and there is then no trace of the alimentary canal in front of the stomach 

 (fig. 8). 



This condition is found in large and strong animals, which have the appearance of 

 having plenty of food in the stomach. I have seen no trace of reduction of any other 

 organs. Simplex forms of several species have been seen in the egg. 



I have very frequently noticed that animals in this condition were about to moult, 

 though I doubt if this is invariably the case. 



Richters (31) regards them as parallel forms, and thinks that some species at least 

 (e.g., M. hufelandi) have peculiar forms of eggs from which the simplex individuals come. 



The fact that the most fully reduced individuals have no anterior opening to the 

 alimentary canal convinces me that the state is temporary. The alimentary canal is a 

 cul-de-sac, opening only by the anus, and it is impossible that they can imbibe food. 



As it is definitely known that some species at least undergo simplification in the 

 course of encystment, it may be supposed possible that the simplex individuals may be 

 about to encyst, or may just have emerged. 



M. dispar retains all the parts of the manducatory apparatus till the inner case of 

 the cyst is formed, and in the same species the individuals which were seen to emerge 

 naturally from the cysts had also all their organs. 



If this is the normal course in other species, we can only connect the ordinary 

 simplex form with encystment by supposing that the absorption of the organs had 

 been prematurely stimulated, or the moult and encystment somehow retarded. 



The Moulting of Acarina. 



A somewhat analogous simplification has been observed among certain of the lower 

 Mites. 



When moulting, these Mites become inert for a time, and return partially to an 

 amorphous condition. Michael (23), p. 180, etc., quotes various authors who have 

 written on the subject. 



Gudden (18), p. 284, writing of certain parasitic Sarcoptidse, states that at the 

 moult the whole of the inner parts of the creature return to an amorphous mass, like 

 the egg ; and that from this the new creature is formed, as from an egg. 



Megnin (22), p. 214, confirmed this view, and believed that at the ecdysis in all 

 Acarina, all the internal organs liquefied and formed a sarcodic plasma, having a true 

 blastoderm, which sprouted like that of an egg. 



By this theory it appears almost as if the whole substance of the animal went to 

 form a single egg. 



Michael (23), p. 181, says that this theory has now been shown to be incorrect, 

 " and that the return to a more or less amorphous condition is usually, and probably 

 always, confined to the soft parts of the legs and trophi, and what may be described as 

 appendages or external organs." 



TRANS. ROY. SOC. EDIN., VOL. XLY. PART IV. (NO. 31). 122 



