94 



ARACHNIDA. 



habits of the parent. They are found in decaying wood, in damp 

 earth, on the under surfaces of stones, in dung-heaps, on leaves, 

 fruit, etc. Some, but by no means all, parasitic forms lay their 

 eggs on or in the body of the host. The eggs are at times laid in a 

 heap, at other times separately; in the latter case they are often 

 stalked ; those of Myobia musculi have a process at the posterior pole 

 by which they are attached to the fur of the mouse. According 

 to Hallbr, many Oribatidae carry their eggs attached to their backs, 

 others are said to lay them in a part of their cast-off chitinous 



Fig. 49.— Cleavage ami formation of the blastoderm in the egg of Tetranychus tdarius (after 

 Clapar£de, from Balfour's Text-book). The yolk-granules are represented by clear circles 

 (in .-1 and D). The nuclei, with the clear areas of protoplasm around them, are much larger 

 than the granules. C, an egg in the stage of blastoderm-formation. 



integument.* The form of the eggs is most commonly elliptical 

 (Fig. 50), sometimes oval, and more rarely globular (Fig. 49), or 

 even discoidal. For their size, they are richly provided with food- 

 yolk. 



1. Embryonic Development. 

 The embryonic development in these eggs is difficult to follow 

 on account of their minute size, and is therefore not well known. 



[Neither of these assertions is quite correct. The carrying of the eggs is 

 almost entirely confined to the genus Damaeus — it is most commonly the 

 immature individuals, not the adults, which pile the eggs on their backs; it 

 is manifest that at this period they cannot have any eggs of their own to carry. 

 What happens is that the larvae are born with soft abdomens, and have the 

 instinct of piling upon their backs dirt, rubbish, etc., as a protection ; they will 

 pick up and carry the eggs and empty egg-shells, from which they may them- 

 selves have emerged, but they will equally pick up and carry the eggs of other 

 Acarina. The statement concerning the eggs being found in the cast integument 

 has never been confirmed, and is very doubtful. — Ed.] 



