506 



SCIEXCE. 



[Vol. VII. , No. 174 



slight pressure of the abdomen in the fresh specimen. 

 This opening extends back about an eighth of an 

 inch, and, on being carefully pried open, shows two 

 closely folded tufts of fine blackish hair. Pressure 

 upon the abdomen will generally force out these 

 tufts, and, if rightly applied, will result in the 

 extension of two orange tentacle like structures, 

 fully half an inch in length, united at the base, and 

 spreading backward and outwardly in a gentle curve. 

 The tufts of hair diminish as the tentacles are ex- 

 tended, the individual hairs occupying small but dis- 

 tinct papillae on the sides, until, when fully extended, 

 they are evenly distributed around them, and uo 

 trace of the brush like tuft remains. If the press- 

 ure be removed, the tentacles contract, the hairs 

 again forming a tuft. 



Specimens of Pyrrharctia isabella, when closely 

 examined, showed a similar abdominal structure ; 

 but here there were four tufts extended instead of 

 two, and in color they were snow-white. Properly 

 applied pressure resulted in the inflation, first, of two 

 basal sacs, which, when fully dilated, could be com- 

 pared to nothing better than the ends of two thumbs 

 pointing in opposite directions, the hairs of two of 

 the tufts arranged rather densely on the convex 

 outer surface. From the middle of the lower edge 

 of these sacs there extended two tentacles similar to 

 those in acraea, but not so long ; and instead of 

 being evenly clothed with hair, in this species the 

 lower portion only has the papillae and hairy sur- 

 face. The sacs and tentacles here are whitish, in- 

 stead of orange, as in acraea. The processes of the 

 latter species have a most remarkable resemblance 

 to the tentacles of the larva of the common Papilio 

 asterias, both in color and in shape. In both species 

 an intense odor, somewhat like the smell of laud- 

 anum, is apparent when first the tentacles are ex- 

 posed : and there is no reasonable doubt but that 

 they are odor-glands, though exactly what purpose 

 they serve is not so clear. In closely allied species 

 no trace of this structure has been detected. Several 

 fresh specimens of Arctia, Spilosoma virginica, and 

 Hyphantria textor showed no trace of it ; and no 

 dry specimens of any other species thus far ex- 

 amined have a similar structure. 



John B. Smith, 



Assistant curator. 



U. S. national museum. 

 Washington, D.C., 31ay 23. 



Muscles of the hind-limb of Cheiromeles 

 torquatus. 



I desire to place on record some observations I have 

 recently made on the muscles of the hind-limb of 

 Cheiromeles torquatus. This bat is one of the most 

 interesting of the Cheiroptera. It is to a great ex- 

 tent arboreal in its habits. The wings are small, the 

 body heavy and uncouth, and the wing-membranes 

 are so arranged as to accommodate the young within 

 a pouch on the back instead of on the front of the 

 chest, as is the case in most of the bats. As a con- 

 sequence, I expected to find in the musculature of 

 the hind-limbs structures recalling those of other 

 orders of mammals rather than those of the bats 

 generally. In the main these anticipations have 

 been met. It has always been supposed that the 

 popliteus, the biceps, the soleus, and plantaris 

 muscles are absent in the bats. It is true that Mac- 

 alister finds in Vampyrops a few oblique fibres ' like 



a rudimental popliteus,' and Humphry identifies a 

 small fascicle in Pteropus as biceps : but with these 

 exceptions, as Macalister says, "there is no trace of 

 biceps, popliteus, soleus, or plantaris in any." There 

 is no doubt that the popliteus, the biceps, and the 

 plantaris are present in Cheiromeles. The soleus is 

 the only one of the absentees which is unaccounted 

 for. 



The maintenance of this group of muscles in a bat 

 which is specialized for a tree-life, and scurries about 

 the trunk after a fashion much like that of Pteromys, 

 suggests the conclusion that the muscles named (ex- 

 cepting the soleus) are essential to the simplest ex- 

 pression of a true act of walking. They are absent 

 in the volant bats, since they are of no use in flight ; 

 but they at once re-appear when the limbs are used 

 for walking, or for the movements which are similar 

 to this act. The assumption here taken that Cheiro- 

 meles is a true bat, which has been specially modified 

 from the typical bat, is, I believe, tenable, and need 

 not be here discussed. Occasion will be taken in due 

 time to present arguments to sustain it. I will be 

 content now to record the existence of the muscles 

 named, and to give brief descriptions of them. 



The popliteus is a well-defined muscle which slightly 

 overlies the origin of the tibialis posticus. It does 

 not create an oblique line on the tibia, which is so 

 characteristic of the muscle in the mammals gen- 

 erally. 



The plantaris is a conspicuous muscle, and is larger 

 and heavier than is the gastrocnemius. It is distinct 

 from the gastrocnemius its entire length. The muscle 

 passes down to the sole of the foot, where it is con- 

 tinuous with the plantar fascia. Traction on the 

 muscle flexes and abducts the foot. 



A single muscular mass attached to the ischium 

 represents the semi-membranosus and the biceps. 

 The biceps becomes free at the upper fourth of the 

 thigh, and is inserted into the head of the fibula. 



The muscle which represents the tibialis posticus 

 and flexor longus digitorum arises from the upper 

 part of both the tibia and the fibula. It remains 

 fleshy until it reaches the neighborhood of the tarsus, 

 when two distinct tendons appear. One of these 

 may be said to represent the flexor longus digitorum. 

 It passes superficially over the ankle, and is lost 

 on the plantar surface. Traction on the tendon ab- 

 ducts the foot, but does not flex the toes. The 

 tendon of the tibialis anticus is lost on the tarsus. 

 Traction on this muscle exerts no apparent influence 

 on the movements of the tarsus. 



Harrison Allen. 



Philadelphia, May 25. 



Double vision. 



In your issue of May 14, p. 440, Mr. Keller de- 

 scribes some phenomena of binocular vision, and 

 asks an explanation. It would be impossible to do 

 this in a short communication, but he will find the 

 subject explained in any work on binocular vision. 

 Perhaps the most accessible to him is my owu little 

 volume, entitled ' Sight' (International scientific 

 series, vol. xxxi.). For explanation of phantom 

 images, I would refer him to the chapters on ' Single 

 and double images,' and on ' Superposition of ex- 

 ternal images,' and especially to the diagram on p. 

 116 ; and for explanation of inequalities of surface 

 of such images, to p. 141 and preceding pages. 



Joseph LeConte. 



Berkeley, Cal., May 24. 



