I'^IO Journal of Applied Microscopy 



The author considers that there is no other source of leucocytes in the 

 vertebrate body for several reasons. 1. The first leucocytes clearly rise from 

 the thymus, as there are no others present in the body when this organ first forms 

 such structures. These first or parent leucocytes quickly infiltrate the blood, and 

 other lymphoid tissues rise in all probability from such migrating cells. 2. No 

 other lymph organ is known which resembles the thymus in origin and develop- 

 mental history. 3. The thymus alone is sufficient to account for all the leucocytes 

 of the body and it is an organ characteristic of all true vertebrates. 4. Except in 

 the case of paired or metameric organs it is not usual to find the same function 

 in any two organs of the body. The thymus is a paired metameric structure of 

 the branchial region only. That the thymus should be the parent source of 

 leucocytes explains its functional activity in young animals and its later atrophy. 



A. isi. c. 



Folsom J. W. The Development of the -pj^g q^^- ^ ^f ^^e paper was twofold, 

 Mouth Parts of Amirnia marjti7na, Guer. -^ *^ ' 



Bull, of the Museum of Comparat. Zool., to supplement a previous account of the 

 Harvard College, 36: 87-157,8 pis., 1900. anatomy and functions of the mouth- 

 parts of a representative collembolan and to discuss the morphology of mandibu- 

 late mouth-parts of insects and their nearest allies upon anatomical and 

 embryological evidence derived from the most primitive insects, the Apterygota. 

 Material was killed in hot water and carried through successive stages of alcohol 

 to be preserved in absolute alcohol. Material was imbedded in hard paraffin 

 and sections cut from 5-10 }x in thickness. Delafield's or Kleinenburg's 

 haematoxylin followed by safranin, Grenacher's alcoholic borax-carmin, and 

 Heidenhain's iron-haematoxylin were used for staining. 



Nine consecutive stages were taken for representing the development stages, 

 and the following parts are considered : The procephalic lobes, labrum and 

 clypeus, antennae, premandibular appendages (intercalary), mandibles, lingua and 

 superlinguae, maxillae, labium, skull, tentorium, segmentation of the head. 



The proto cerebrum of the Apterygota agrees with that of other insects in 

 development and structure. The ocular segments of the Hexapoda and decapod 

 Crustacea, as well as the compound eyes of the two groups, are homologous. 

 The labrum and clypeus of insects develop from a single median evagination 

 between the procephalic lobes, and do not represent a pair of appendages. The 

 labrum of Apterygota is homologous with that of other insects, and of the 

 Symphyla, Diplopoda, Chilopoda, and higher Crustacea. The antennae of the 

 Apterygota evaginate from the posterior boundaries of the procephalic lobes, 

 and agree with those of the Pterygota. In both groups the antennae are first 

 post- and later pre-oral in position. The dentocerebrum of insects is homologous 

 with that of Crustacea, and the antennae of Hexapoda are equivalent to the 

 antennules of Crustacea, and the embryonic pre-antenncX' of Chilopoda. Pre- 

 mandibular or intercellary appendages exist in the embryo of Anurida, and 

 appear to be represented in the adults of several Apterygota genera. The trito- 

 cerebrum of Apterygota is homologous with that of Orthoptera and decapod 

 Crustacea, and the rudimentary premandibular appendages of Collembola and 

 Thysanura represent the second antennae of decapod Crustacea, and probably 

 the antennae of Diplopoda and Chilopoda. A distinct ganglion for the intercalary 



