THE ENCYSTMENT OF MACROBIOTUS. 9 



the product of a secretion from the skin. Fragile though it is, 

 it may be a sufficient protection to the inner cyst against the 

 only enemies likely to be attracted by Water-Bears. 



Extraordinary though it may appear that an animal so high 

 in the scale as an Arthropod should lose all its internal organs 

 in the course of encystment, a well-known phenomenon in the 

 same group (Tardigrada) supports the belief that this really 

 happens. Nearly all species of Macrobiotus are known to have 

 what Eichters calls "simplex" forms. The teeth in these are 

 reduced in size, and the rods in the pharynx are absent. Prof. 

 Eichters appears to have seen no further simplification, but in 

 Scotland it is common for the whole alimentary canal in front 

 of the stomach, with all its adjuncts, to be absent. There is no 

 mouth, no gullet, no teeth, but some trace of the pharyngial 

 bulb usually remains. We find large, strong, active animals 

 whose stomachs appear distended with food, yet which possess 

 no organs for imbibing food. No conclusion seems tenable but 

 that reduction must have taken place since the food was imbibed, 

 but this explanation is itself inexplicable, and we are further 

 puzzled when we find that some eggs produce simplex forms. 



The applicability of the term "encystment" to the process 

 which has been described may be questioned, but the word 

 "cyst" well describes the bodies formed; and, moreover, the 

 formation of outer envelopes, within which the whole substance 

 of the animal passes into an apparently simpler condition, offers 

 sufficient analogy with encystment as we find it in the Protozoa 

 to justify the adoption of the term. 



The formation of the cysts was going on in the beginning of 

 winter, in October and November. This may indicate that it is, 

 like the production of winter-eggs by various animals, a means 

 of preserving the species through the rigours of winter. 



M. dispar is the only species in which the complex process 

 has been traced so far as the simplex form within the inner cyst. 

 Cysts similar to the inner cysts of M. dispar are known in several 

 species. Among moss brought by Mr. W. S. Bruce from Spitz- 

 bergen in August, 1906, and examined in September, there were 

 many cysts which were shown by the pharynx and claws of the 

 contained animal to belong to M. echinogenitus, Eichters. More 

 recently the formation of the cyst of this species has been seen 



