ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 287 



limb after their first appearance. There were striking differences in the 

 •endocrine glands, bnt no constant variation from the normal was 

 observed in the gonads. 



Influence of Diet of Ductless Glands.* — E. R. Hoskins finds that 

 thyroid feeding causes little or no change in the body-weight of growing 

 ••albino rats. It produces decided hypertrophy of heart, liver, spleen, 

 kidneys, and suprarenal bodies (especially in males). Thymus feeding 

 has no apparent effect on the growth rate of the body. Nor did feeding 

 with hypophysis or with pineal body make any apparent change. Many 

 ^detailed results are communicated. 



Undersized New-born Rats.f — Helen Dean King discusses the 

 occurrence of undersized and abnormally light new-born mammals, 

 which breeders call "runts," and discard from breeding. A litter of 

 rats may contain individuals of three kinds as regards their inherent 

 ■capacity for body-growth. As a rule all are normal. Occasionally 

 some have a very small birth-weight, but recover from this. If a litter 

 is very large, or if the mother is not in good physical condition during 

 the gestation period, some of her young may be born with their growth 

 •capacity so impaired that it is impossible for them to grow beyond a 

 •certain stage. These individuals are true " runts." They tend to have 

 an abnormally small nervous system when they become mature. They 

 are lacking in reproductive vigour, so that they are usually unable to 

 reproduce their kind, and so prove a menace to the colony in which 

 they live. 



Origin of Osteoclasts. J — L. B. Arey has followed up and extended 

 the investigation left unfinished at the death of Professor C. W. Prentiss, 

 on the origin and fate of the osteoclasts. These may arise in the 

 earlier stages of development from the reticular cells of the marrow ; in 

 later stages they are formed from sycytia of exhausted osteoblasts. The 

 numerous nuclei of large osteoclasts are derived : («) from the 

 ■constituent osteoblasts, and (b) from bone-cells which are ingested as 

 the bone-matrix is re-absorbed. There is no direct evidence that the 

 ■osteoclasts are the active agents in bone-resorption ; they may also bo 

 interpreted as degenerating osteoblasts. Eventually the osteoclasts 

 ■either atrophy and disappear, or are resolved into the reticulum of 

 bone-marrow. 



Origin of Vascular Endothelium and of Erythrocytes. §— Franklin 

 Pearce Reagan has made experimental studies on embryos of chick and 

 ^teleosts. One view is that the earliest vascular tissue appears on the 

 yolk-sac (as an angioblast primordium), and grows towards the embryo. 

 On reaching the embryo's body the vascular tissues permeate the intra- 

 •embryonic tissues in a centrifugal manner, forming the entire lining of 



* Journ. Exper. Zool., xxi. (1916) pp. 295-346 (4 charts). 



t Anat. Record, xi. (1916) pp. 41-52. 



X Anat. Record, ii. (1917) pp. 319-22. 



§ Amer. Journ. Anat., xxi. (1917) pp. 39-174 (22 ph.). 



