ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 285 



preparations show closed ring strnctiires. In the tubules of the adult 

 mammalian testis, completely teased, no blind endings, buds, nor ring 

 formations were observed. In a cryptorchid of the rabbit, as described 

 by Huber and Curtis, extended anastomoses of testis tubules were 

 observed in two regions of the tubule complex, and in two regions, near 

 the periphery of the gland, tubnles were joined so as to form two folded 

 rings. The preparations from the cryptorchid of the rabbit present 

 appearances hot unlike those shown in teased preparations of the 

 seminiferous tubules of the bird. The presence of the remains of the 

 embryonic network of the seminiferous tubules in the cryptorchid of 

 the rabbit and in the bird's testis, postulates a relatively late complete 

 morphogenesis of the seminiferous tubules of the mammal. Phylogeny 

 and ontogeny indicate this. 



Age and Fertility in Rats.* — Helen Dean King has studied the 

 litter data of 76 female rats, extracted strains derived from the second 

 filial generation of a cross between the wild Norway rat and the 

 domesticated albino. The material comprises the data for 585 litters, 

 including 2036 males and 1910 females. The average number in each 

 litter was 6*7. Fertility in the rat, measured by the total number of 

 litter -i cast, increases with the age of the female rat up to seven months, 

 the climax of reproductive activity. There is a sharp decline after the 

 female is a year old, and the menopause appears at eighteen months. 

 The age iniluences the size of the litter. The average number of 

 litters is 7*7 per female. The sex ratio for 3955 individuals was 

 106 '1 males to 100 females. The age of the mother does not seem to 

 be a dominant factor in determining the sex of her offspring, but old 

 females seem to produce relatively more female than male offspring. 



History of Eye Muscles.f— H. V. Neal has sought to demonstrate, 

 on the basis of embryological evidence, the exact homology of the first 

 three permanent myotomes of Amphioxus, Petromyzon and Squalus. 

 He maintains, with Dohrn, that the second as well as the third myotome 

 participates in the formation of the external rectus muscle. He suggests 

 that the text-book formula for the ontogenesis of the eye-muscle should 

 be read thus: From the first myotome (pre-mandibular head-cavity) 

 arise the muscles innervated by the oculo-motor. From the second 

 myotome (mandibular head-cavity) develop the obliquus superior and 

 the ventro-lateral portion of the M. rectus externus. From the third 

 myotome (hyoid head -cavity) arises the dorso-median portion of the 

 rectus externus muscle. 



Rare Form of Double Monstrosity. J — James F. Gemmill and 

 James Stewart describe a " Siamese Twin " omphalopagous human 

 monstrosity which (with ' one doubtful exception) appears to be of a 

 unique type. The peculiarity is that the union is confined to the 



* Anat. Record, xi. (1916) pp. 269-87 (3 figs.). 



+ Anat. Record, ii. (1917) pp. 391. 



; Journ. Anat. Physiol., 1. (1916) pp. 316-23 (4 figs.). 



