Miscellaneous. 99 



of nerves, as in insects — two for the labium (nervi labii inferioris), 

 two for the maxillce (nervi maxillares), and two for the mandibles 

 {nervi mandibulares). The third ganglion of the head, which I 

 propose to name the pedomaxillary ganglion, rests upon a peculiar 

 lamina, the pedomaxillary plate *, and it furnishes one pair of nerves 

 for the two jaw-feet (nervi pedomaxillares). The trunk possesses 

 seven ganglia ; that is to say, there is a ganglion for each segment. 

 The first ganglion of the trunk is very small, although larger than 

 the pedomaxillary ganglion ; all the other ganglia of the trunk 

 havo the same volume. From each of these ganglia originates a 

 pair of nerves for the feet — connectives separate from the nerves 

 for the muscles and the skin of the segment, as described by H. 

 Itathke. In this respect the pedomaxillary ganglion perfectly 

 resembles those of the trunk ; for, besides the nerves of tho jaw-feet, 

 it emits two other nerves for the posterior part of the head. It 

 would seem, as shown by the innervation and the presence of a 

 distinct ganglion, that the posterior part of the head of Idothea is a 

 thoracic segment amalgamated with the head. The latter is there- 

 fore an imperfect cephalothorax, but still morphologically different 

 from the heads of insects. There are four postabdomiual ganglia, 

 which are much smaller than the ganglia of the trunk ; the last is 

 the largest ; the others are of equal size. The first, second, and 

 third only furnish one pair of nerves for the corresponding seg- 

 ments : while the last emits four pairs of nerves. There is also a 

 sympathic nerve, represented by an unpaired trunk, placed be- 

 tween tho connectives of the ganglionic chain, and interrupted by 

 the ganglia— that is to say, exactly the same as that which F. 

 Ley dig has described in Porcellio se-aber f , llathke saw it, but did 

 not recognize it as the sympathic. — Comptes Rendus, March 22, 

 18S0, p. 713. 



On a Peculiar Modification of a Parasitic Mite. 

 By M. M£gnin. 



In a great many insects parasitic on plants, the female, when 

 ready to deposit her eggs or to give birth to larvse, is seen to cover 

 herself with a cottony or byssoid secretion, which serves not only 

 to protect herself, but also to preserve her progeny from any injury 

 during the first period of life. This is observed in most cochinoal 

 insects and in the woolly Aphis. 



Certain Arachnida, also plant-parasites, possess the same pecu- 

 liarity ; and a species of Tetranychus has received its name (T. 

 telarius) precisely on this account. In this case the cottony secre- 

 tion of the mite forms a true nidification, destined to protect the 



* E. Brandt, ' Ueber eiue Cephalothoracalplatte des gemeinen Schacht- 

 wurmes (Idothea entomon), St. Petersburg, 1877. 



t Vom Bau des thierischen Korpera (Tubingen, 18G4), p. 251 ; and 

 Tafeln zur vergl. Anat. pi. vi. fig. 7. 



