INVERTEBBATA, CRYPTOGAMIA, MICROSCOPY, ETC. 625 



or to give birth to larvae often covers herself with a cottony or byssoid 

 secretion, which serves not only to protect herself, but also to pre- 

 serve the young during the early periods of life. Certain Arachnids, 

 also parasitic on plants, have the same power ; and a species of 

 Tetranychus has for that reason been named T. telarius. In this case 

 the cottony secretion constitutes a true nidification destined to protect 

 the eggs, as the female lays successively in several nests. 



Hitherto nothing similar had been observed amongst the Acarians 

 parasitic on animals ; but M. Megnin has now found by accident an 

 exactly similar fact in the parasite of a bird. In dissecting an 

 American Grosbeak he was struck by the presence of numerous white 

 spots strewn over the naked median and sternal portion of the skin 

 covering the lower surface of the breast. Viewed with a lens they 

 appeared like spots of mould ; but under the Microscope, especially 

 after soaking them in glycerine, which rendered them diaphanous, 

 these spots proved to consist of a fine tissue, under which appeared 

 a group of eggs in different stages of incubation, of empty egg- 

 shells, and of small yellow Acarians just hatched. These Acarians 

 are but octopodal larvse, which it is easy to recognize by the anatomical 

 characters of their rostrum and legs as belonging to the species named 

 by the author Cheyletus lieteropalpus* 



Professor Ch. Eobin f has shown that the plumicolous Sarcoptides 

 lay their eggs in small masses at the axils of the barbs of the feathers ; 

 and M. Megnin thought that his parasitic Cheyletidae did the same, 

 though he had never found their eggs together. 



The foregoing observations show how these eggs, which are very 

 large ('IS mm. x '11 mm.), are laid, and what precautions the 

 animals take to protect them, a fact which brings them singularly 

 near the Tetranychi, with which they are besides so closely allied 

 in organization ; they show, moreover, that the larvae of this species 

 are octopod at birth, a character not possessed by those of the 

 Tetranychi, nor even by those of the wandering Chcyletides, such as 

 Cheyletus eruditus. 



Structure of Trombidium.l — The results of A. Croncberg's in- 

 vestigations lead him to believe in a closer connection between this 

 genus and the Hydrachnidai than would apjicar from Pagenstecher's 

 monograph of the genus. His study of T. holosenceum shows that the 

 cuticle consists of an external layer, traversed by pores and carrying 

 the hairs, and of a thin fenestrated inner layer. The hypodormis is 

 granular, semi-fluid in life ; no cell-structure can be discovered in it. 



Dlijedive Organs. — The labium presents a deep groove, open in 

 front. Posteriorly, its halves are united by a cross-piece, from each 

 side of which a narrow piece runs backwards along the uppi:r edge of 

 the maxilla, representing the-" supra-cesophagcal ridges " of ////(/ntc'/jmi 

 glohosa. Closely connected with the ci'oss-picco arc two chitinous 

 tubes, which jiroject backwards and enclose the posterior three-iniartcrs 

 of the two great tracheal vessels, the anterior part of these being left, 



* ' Joiirn. Aniit. ct I'livsiol.' (Uoliin), 1878. 



t ' ("c.iiiptu.s llLMi.his,' Apr. :!(), ISCS. 



X 'liiill. S.m;. Iinp. Nat. Mascow,' liv (187!t) i- 2[H 

 VOL. III. 2 T 



