SCOTTISH TARDIGRADA, COLLECTED BY THE LAKE SURVEY. 657 



One of these appears to be more constantly blue than the others. This was erroneously 

 recorded as M. islandicus (6), trusting to the blue colour and the pharynx. It is now 

 known to lay smooth eggs in the skin, and is therefore quite distinct from M. islandicus. 

 The blue colour is found in large granules, of nearly uniform size, densely filling the 

 cells. The colour is sometimes modified by a distinct green tint in the most anterior 

 and posterior cells. 



Simplex forms. — No explanation has yet been offered of these curiously reduced 

 forms. Richters, without attempting to account for them, regards them as parallel 

 forms, comparable with the various castes of bees and other sociable insects. This 

 implies that they are permanent, and that the peculiarity continues throughout life, and 

 this view is supported by the fact that in some species Richters has seen the simplex 

 form emerge from an egg slightly different from the typical egg of the species. In this 

 view of their permanence I cannot concur, basing the opposite opinion on the fact that 

 the simplification may go so far as the total disappearance of the alimentary canal in 

 front of the stomach, with all its accessory organs. Large well-nourished animals, with 

 stomachs full of food, and no mouth or gullet, obviously cannot have been long in that 

 condition. I have suggested (6) that this change is correlated with moulting, and I 

 still think that this is the general fact, though it cannot apply to the simplex forms in 

 the egg. In view of the investigations into the encystment of Macrobiotus now going 

 on in various quarters, the connection of simplex forms with moulting may have a 

 possible meaning. The simplification which happens during encystment is carried 

 much further than in the ordinary simplex forms, involving the loss of claws and 

 stomach as well as pharynx. There is at least a very striking parallel between the 

 two phenomena, and it may prove to be more. If the encystment is demonstrated to 

 be, as among lower forms, really a kind of rejuvenescence, and if this requires the 

 absorption of all the organs and their re-creation anew, then the simplex forms might be 

 individuals in which the absorption had been stimulated prematurely before the 

 moulting, which usually precedes it, or, conversely, that the moulting had been retarded. 



Encystment. 



It has recently been discovered that certain species of Macrobiotus encyst them- 

 selves. Professor Lauterborn published the first note on the subject (5). The animal 

 forms within the skin, which is loosened as for an ordinary moult, an elliptical yellow 

 cyst, within which, in one species at any rate, it undergoes a curious metamorphosis, 

 losing all its conspicuous organs. The process is not fully understood, and has never 

 been completely traced. What happens next, after the reduction above referred to, is 

 unknown. The escape of animals from cysts has been seen by Professor Richters and 

 myself, but in no case could we tell whether these animals had ever undergone 

 reduction. I am inclined to think that these escapes have been premature, and due to 

 stimulation by the unnatural heat of a room. In one species, M. dispar, recently 



TRANS. ROY. SOC. EDIN. VOL. XLV. PART III. (NO. 24). 93 



