260 



KNOWLEDGE. 



[NOVEMBBE, 1903. 



This instance, it may be observed, affords a warning 

 against drawing iuferences, like the one quoted above, 

 with regard to the powers and habits of animals on wholly 

 iusutiicient data. 



Before dismissing this part oi' the subject, reference 

 may be made to a jieculiarity in the structure of the teeth 

 of baby bats, which appears to be correlated with their 

 abnormal mode of life. It is well known that in the 

 majority of mammals the milk or baby teeth differ some- 

 what in foi-m from their permanent successors, but 

 the differences are comparatively small, and both series 

 arc of the same general type. In bats, on the contrary, 

 the milk-teeth are utterly unlike those of the permanent 

 series ; being slender, with sharp, hook-like cusps — in 

 fact, just such a type as would be adapted for obtaining a 

 firm hold of the nipples of their parent while she is in 

 flight. And there is every probability that this is their 

 true function. Possibly, indeed, baby bats niiy hold on 

 to the maternal nipp es during the whole time that they 

 are in the air, as was found to be the case with the young 

 of the New York female. It is also significant in this 

 connection that bats shed their milk-teeth at a relatively 

 early age — not improbably at the time when they learn 

 to shift for themselves. 



Such, then, are the leading facts in regard to what is 

 known of the nursery arrangements of ordinary bats. 

 There is, however, one very remarkable — and, it may 

 be added, very ugly— bat which has struck out a line 

 altogether of its own in this respect, for a parallel to 

 which w^e must go to the marsupials. The species in 

 question is the naked but (C/iiromeles torquata), of the 

 Malay countries, which is the only representative of a 

 genus whose nearest relatives are the mastiff- bats of 

 tropical America. 



In this large and hideous sjsecies the thick skin is 

 almost entirely naked, and thrown in the chief regions of 

 movement into a number of deep wrinkles and folds. 

 But its most peculiar feature is the presence on the chest 

 and under the wings of large pouches in which are 

 placed the nipples ; these nursing pouches being present 

 in both sexes. These pouches, writes Dr. Dobson, " are 

 probably absolutely necessary for the preservation of the 

 young, which could scarcely otherwise succeed in main- 

 taining its hold on the naked body of the mother during 

 flight. It is interesting to find these pouches developed 

 in both male and female, for their presence in the former 

 suggests the idea that, where two young are born together, 

 the male may relieve the female of the charge of one of 

 them." 



So far as I can ascertain, nothing is known with regard 

 to the breeding habits of this bat, and it is consequently 

 quite uncertain whether twins are ever produced. Whether 

 there is any truth in Dr. Dobson's suggestion must there- 

 fore, for the present at any rate, remain undecided. It is, 

 however, quite conceivable that the presence of the pouch 

 in the male may not be connected with the nursing 

 function, but may be an acquired secondary sexual 

 character analogous to the presence of horns in the 

 females of many antelopes and the reindeer. So far as it 

 goes, the case of the American Lasiurus borealis is against 

 the theory that the males of any species of bat undertake 

 the duties of a foster-mother, since it is clearly demon- 

 strated that the weight of even four young ones is no 

 hindrance to the activity of the female. From the nature 

 of the case it would, however, be a very difficult matter to 

 prove that Dr. Dobson"s theory with regard to the naked 

 bat is or is not true. To pi-ove it true, a male must be 

 taken with a young one in its pouch, while to demonstrate 

 that it is false, a female must be cajjtured with a pair of 

 yoimg bats in the same receptacle. And since it is highly 



likely that the birth of twins is a rare event (even if it 

 ever occurs), the chances of either of these discoveries 

 being made would appear to be extremely remote. 



Apart from the question whether or no the male acts as 

 foster-mother, the discovery of a naked bat with young in 

 her pouch would be of extreme interest from another point 

 of view. The young of ordinary bats are Iwrn in an advanced 

 state of development, with their eyes open and their bodies 

 oovei'ed with hair, as indeed is absolutely essential 

 owing to the nature of their environment and the active 

 muscular powers they have to exert soon after their entry 

 into the world. But the young of the naked bat would 

 seem to have no need either of protection from cold or of 

 active muscular exertion during its sojourn in the nursing- 

 pouch. Is it then born naked, or does it when just 

 formed retain the hairy coat of the ancestral type from 

 which it is descended ? Some might even go so far as to 

 suggest that the young of a bat thus specially protected 

 as soon as it enters the world would ba born in a helpless 

 condition recalling that of young marsupials ; biit there 

 are considerations which render this idea improbable. 



Conducted by M. I. Cross. 



" Sprixg-tails." — While examining some duck weed (lemiia), 

 a number of minute black insects were noticed which continually 

 jumped and sprang in all directions. These turned out to be 

 specimens of Poiliii-a aqdut/ca, commonly called " Spring-tails," 

 a low type of insect life, in which the mouth parts have 

 degenerated, a coUophore, or sucker, has developed on the ventral 

 side of the abdomen, and the caudal spines present in some 

 nearly related fpecie.s have been modified into an apparatus 

 placed under the abdomen, which jerks the insect suddenly and 

 sharply into the air. Podara (jquatica is very small, ^\ of an 

 inch long, and several can be kept alive in a cell and examined 

 from time to time under the microscope. This is most 

 interesting, as their movements are slow, except when the spring 

 3. 



Fig. 1. — " Spriug-tail," Podura aquatica, dorsal view. Fio. 2. — 

 Ventral view of P. aquatica, showing the mouth, the collophore, and 

 the "spring" in its normal position. Fro. 3. — Lateral view of the 

 posterior end of the inaect, showing the position of the spring on 

 bemg released. Fio. 4. — One of the claws, showing the gland and 

 perforation. 



comes into action, and their appearance grotesque and quaint. 

 Sometimes they crawl on the surface of the cover-glass, and this 

 gives an opportunity to examine the ventral side, and the 

 spring aad sucker. Both sides of the body are shown in the 



