642 ARACHNIDA. 



The maxillae and mandibles finally unite to form a beak (R 

 Fig. 6) and the three pairs of feet (p l -p 3 ) are folded along 

 the median line of the body. The farther development of the 

 embryo is now for a time arrested, and a peculiar tooth-like 

 process (Fig. 7, d) is developed. Claparede thinks that by 

 means of this the anterior end of the egg-shell is cut off, and 

 the embryo protrudes through, when, as in Fig. 7, it is seen 

 to be surrounded by a new membrane, the deutovum (eft), 

 equivalent to that of Atax. The front pair of legs (p 1 ) have 

 grown larger and stand out in front and on each side of the 

 beak (R). The growing embryo again forces off the anterior 

 end of its deutovum, and the oval end of the egg protrudes 

 through, and is surrounded by another membrane. This is the 

 tritovum. The embryo is now surrounded by the membrane 

 of the tritovum, and also by the deutovular membrane and the 

 original egg-shell, the last two having lost a small portion of 

 their anterior ends. During the tritovum-stage the fore pair 

 of feet become curved in like claws, and the beak sinks down 

 into the body. 



Now the six-footed larva (Fig. 8) breaks through the shell 

 and closely resembles the adult (Plate 11. fig. 9). The first 

 pair of feet, modified for grasping the hairs of the field-mouse, 

 on which it is a parasite, take the place of the maxillne, which 

 have been arrested in their development, and the mandibles 

 (pr) assume a style-like form. After one or more moultings of 

 the skin a fourth pair of feet (p 4 ) are acquired, and the adult 

 form results, which the author considers as the type of a new 

 family of Acarina. Claparede also suggests the affinity of 

 Myobia to the Tardigrades (Echiniscus and Lydella), especially 

 from the study of the structure of the style-like mandibles and 

 their supports. We feel convinced, after examining Clapa- 

 rede's figures and descriptions that this comparison is very 

 significant, and this has led us to consider the Tardigrades 

 as a family of true mites, related to Myobia and Demodex. 



A French naturalist, C. Robin, has recently observed in cer- 

 tain bird sarcoptids, to which the parasite of the Downy 

 Woodpecker noticed above is allied, "that the males pass 

 through four, and the females through five stages, indicated as 

 follows : (1) the egg, on issuing from which the animal has the 



