Studies on Thysanuran Anatomy. \i\ 11. T. Fkknam). 



(Pri'Iiiniiiary ('Diniuunlciitlon.^ 



The ini|iortiince of ii cuinplele kMowlcilno of the iirmtoiiiy of the ThyKiiniirii 

 for the intelli<;cnt consideration of (Hiestions relating to insect phylogcny, 

 has led nie to devote consideralilo attention to this group. A more complete 

 paper, of the original portion of wliicli this is but an abstract, is now ready 

 for publication. 



The forms hero considered are Anurida mnritima, and Lepisnia saccha- 

 rina — the former qnite fully, the latter only in a few particulars. 



In Anurida the two pairs of moulhparts — mandibles and maxillae— can 

 be protruded from, or drawn into the cavity of the head where they lie in 

 a sort of pocket, ventral to the pliarynx. The digestive tract is comimaed 

 of three chief divisions — fore, mid and hind gut — separated from each other 

 by structures functioning as valves. The fore gut has no longitudinal mus- 

 cles and the circular fibres have all their nuclei on the middle dorsal line 

 of the gut. In the mid gut no cliititious lining is present, but the free 

 surface of the epithelium is covered by fine hairs which constitute the 

 " Hiirchensaum " described by Frenzel (Arch. f. Mik. Anat., XXVI, p. 229, 

 1886). In molting, the nuclei of these cells divide, and the products of this 

 division pass to opposite ends of the cells. The cells themselves now divide, 

 and the portions nearest the lumen are set free. These form a mass which 

 lies in the gut till the cuticula of the exterior of the body is thrown off, 

 when it is expelled. 



A structure termed by Sommer (Zeits. w. Zool., XLI, p. 683, 1885) the 

 "exkretionsorgane" in Macrotoma, is present in Anurida, and I regard it 

 as homologous with the fat body of the higher insects. Its connection with 

 the hypodermis, Sommer believes, proves that this is not correct, but my 

 specimens appear to indicate that such a relation is only secondary. 



The heart lies on the dorsal middle line, and at its anterior end becomes 

 continuous with the aorta, which passes forward and after a time bends 

 ventrally and rests on the fore gut. Farther forward it entirely surrounds 

 this, and extends below it to the sub-oesophageal ganglion. A little ante- 

 rior to this point it abruptly ends. The nervous system consists of a brain, 

 a sub-cesophageal ganglion and three ventral ganglia, one in each segment 

 of the thorax. No abdominal ganglia occur, but the metathoracic ganglion 

 appears to have resulted from the fusion of at least two. 



In each of the main nerve trunks, near its origin, lies a very large nucleus, 

 more than twice the size of the nuclei of nerve cells, nuclei of the gan- 

 glia or brain. I have been unable to ascertam its significance. From the 

 brain are innervated the antenn.-e and eyes ; from the sub-oesophageal gan- 

 glion, the mouth parts ; from the thoracic ganglia, the different parts of the 

 segments in which they are situated ; the metathoracic ganglion, in addition 

 innervating the abdomen. One or two small ganglia with two or three 

 nerve cells are present in the more distal joints of the legs. Tactile bristles 

 are scattered over the surface of the body, and are especially abundant in 

 the antenme and around the mouth. 



On the terminal joint of each antenna is a small trilobed organ, similar 

 to the bilobed organ describeil for t'arapodea by Kingsley ( Am. Nat., XVII I, 

 p. 540, 1884.) I have traced its connection with a nerve fibre, and am 

 inclined to look upon it as in some way aiding in the determination of the 

 forms of the objects which it may touch. There are five eyes on each side 

 of the head, each consisting of a nearly splierical mass of protoplasm con- 

 taining four nuclei, and covered externally by the cuticula which is here 

 smooth, though bearing small protuberances elsewhere. Immediately be- 

 neath the protoplasm is a dense layer of pigment. The different eyes of 

 each side are entirely independent, and lie some little distance apart. No 

 structure resembling an ommatiileum could be found. 



The post-antennal organ tlcscribed by Laboulb<<ne is situated between the 

 eyes and the biuse of the antenna, on each side of the head. It is a rosette 

 like structure, consisting of from seven to nine ovoid liodies radiating from 

 a centre. At the central end of each is a sort of pedicel or stalk joining the 



