754 Comparative Animal Physiology 



fail to develop after injury to the ovaries by irradiation. In the amphi- 

 pod, Gammarus pulex, suppression of the ovaries by a parasitic worm, Poly- 

 mor'phiis minutus, or by irradiation, has been observed to be associated 

 with failure of the typical marginal bristles of the oostegites to develop. The 

 ability to develop the marginal bristles was restored parallelly with oogenesis 

 after cessation of the irradiation treatments. Female shrimp, Leander, cas- 

 trated by bopyrids or by x-ray irradiation, showed absence of development of 

 the abdominal incubatory chamber and the special guanophores associated 

 with the corresponding abdominal segments.^^- '**' These observations strong- 

 ly support the hypothesis that in these crustaceans the ovaries may produce 

 a hormone normally influencing certain bodily modifications concerned with 

 provision for the developing young. 



In insects, despite extensive observations on the effects of parasitic castra- 

 tion, surgical castration, and gonad implantation, there is no reliable sug- 

 gestion as yet that gonadal or other blood-borne hormones significantly in- 

 fluence the differentiation of secondary sex characters. In fact, strong evi- 

 dence to the contrary is seen in the frequently observed occurrence of gynan- 

 dromophism. 



Gonadotropic Hormonal Activity. Many invertebrates, like the vertebrates, 

 show annual or other reproductive rhythms, with periods of sexual activity 

 alternating with periods of inactivity. In most instances there is as yet no 

 knowledge of the pathways through which the gonads are activated or in- 

 hibited. 



Some recent experiments have indicated that oogenesis in female shrimp 

 of the genus, Leander, is under the control of a hormone originating in the 

 sinus glands.^^**' ^-"' ^-^ This shrimp reaches the end of its breeding season 

 late in the summer, and its ovaries become tremendously reduced in size and 

 activity and normally remain so during the fall, winter, and early spring. 

 Removal of the eyestalks or even removal of only the sinus glands from the 

 eyestalks in such a non-breeding season as September or October results in 

 a very rapid increase in weight of the ovaries, these organs increasing about 

 seventy-fold in 45 days (Fig. 285). Normal eggs may be laid at the end of 

 this period. Unoperated controls show almost no increase during the same 

 period. Implantation of sinus glands into the abdomens of eyestalkless ani- 

 mals will inhibit ovarian development, depressing it even more than is ob- 

 served in unoperated controls. A similar sort of hormonal relationship between 

 the sinus gland and the ovary, with the sinus gland acting as inhibitor for 

 ovarian maturation, has been demonstrated for the fiddler crab, UcaA^^ A 

 similar situation appears to obtain in the crayfish,*'' 



A further reproductive function of the crustacean, sinus gland is ob- 

 served in the fact that female crayfishes bearing eggs on their pleopods nor- 

 mally postpone their spring molt beyond the time of molting of males, and 

 until the young have become free. This adaptive response is apparently the 

 result of activity of a sinus gland hormone, inasmuch as egg-bearing females 

 after sinus gland extirpation molt as readily as do males. 



The majority of species of insects so far investigated show a hormonal 

 relationship between the corpora allata and the ovaries. AUatectomy in late 

 larval stages or young adults is accompanied by a failure of the eggs in the 

 ovary to undergo their normal growth and development. This has been dem- 



