740 Comparative Animal Physiology 



There is a greatly accelerated rate of oxygen consumption and an increase in 

 water uptake. There is also the typical thinning of the exoskeleton result- 

 ing from the dissolving and resorptive activity of the hypodermal cells. All 

 of these results of eyestalk removal are prevented by implantation of sinus 

 glands, and it therefore appears probable that all are under the influence 

 of a single molt-inhibiting hormone from the sinus gland. 



Comparing the abrupt increase in oxygen consumption after eyestalk re- 

 moval with the gradual increase during normal premolt, it appears evident 

 that the normal molt, unlike the experimentally induced one, results from 

 a gradual and slow decrease in the blood titer of the molt-inhibiting prin- 

 ciple from the sinus gland. This difference between normal and experi- 

 mentally induced molt might account in part for the often-reported observa- 

 tion that eyestalkless animals show gready reduced viability, usually suc- 

 cumbing about the time of the first succeeding molt, or, if surviving that, 

 commonly dying during the second. A rare animal survives to the third. It 

 has been shown that the average survival time of eyestalkless animals can be 

 extended from about 17 days to more than 38 by periodic implants of sinus 

 glands. It seems a reasonable supposition that in molting in eyestalkless ani- 

 mals some uncurbed molting processes greatly outrun other more basic un- 

 derlying ones. That some differences from normal molt' do occur is seen 

 in that the exuvia of eyestalkless crustaceans have less inorganic salt content 

 than those from unoperated molting specimens.^"^ The high mortality is as- 

 sociated with factors other than the mere molting. 



The molt-inhibiting hormone from the sinus glands appears to be respon- 

 sible for the failure of egg-bearing female Crangon to molt until the young 

 have hatched, ''*' and for the fact that at the annual spring molt of Camharus 

 the egg-bearing females molt several weeks later than the males qnd only 

 after the young have left the maternal pleopods. Sinus gland removal is just 

 as effective in inducing molt in egg-bearing female crayfishes as is a similar 

 operation in males. ^"'^ 



There is reason to suspect that at least one additional factor, arising in 

 some regioa of the body other than the eyestalks, cooperates in the control 

 of molt. A careful study of the deposition of calcium salts in the gastroliths 

 shows that this process is rhythmical, with rapid deposition during the night 

 and little deposition during the day. Suggestive in this regard, injection of 

 extract of the brain tissue or strong electrical stimulation of the cut ends of 

 the optic nerves of eyestalkless animals wall cause a transitory acceleration 

 in rate of oxygen consumption.^'*^ 



HORMONES AND SEX AND REPRODUCTION 



Vertebrates. The subject of hormones and sex and reproduction in higher 

 vertebrate has been comprehensively reviewed. ^^- ^^ 



The hormones whose primary functions are concerned with sexual repro- 

 duction and care of the developing young may be divided in vertebrates 

 into three general groups. The first of these, the gonadotropins, are hormones 

 which principally govern the development and activities of the primary sex 

 organs, the gonads. The second general group comprises those hormones, of 

 gonadal or other origin, which typically regulate the male and female sec- 

 ondary and accessory sex characters of the body and exercise a control over 



