284 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



dispersed ophthalmoblastic material. It uiav be that indifferent ectoderm 

 is stimulated by a fragment of ophthalmoblastic material too small to 

 differentiate into a morphologically discernible structure. It may be 

 that blastolyzed potential optic cup substance exerts a "lentogenic" 

 stimulus on the ectoderm which is of the nature of a catalytic reaction. 



Development of Vascular System in Reptiles.* — Chas. H. 

 O'Donoghue finds that three of the six embryonic arches persist in the 

 adult reptile, and of their connecting vessels both ductus carotici and 

 ductus arteriosi may persist or be represented by ligamenta. In 

 Sphenodon both ductus are to be found on each side. In Chelonia the 

 ductus carotici are usually absent, while the ductus Botalli remain. In 

 Crocodilia the ductus carotici are probably not usually present, and the 

 ductus Botalli may probably remain. In Lacertilia the ductus carotici 

 are present very generally, although in some species reduced or absent, 

 and the ductus Botalli are always reduced and very often absent. In 

 Ophidia the ductus carotici are normally absent, but the ductus Botalli 

 persist, and often on both sides, in spite of the suppression of one lung 

 and pulmonary artery. There seems little doubt that the main factor 

 affecting the persistence or loss of these structures is the change under- 

 gone in the relative positions of the heart and arterial arches in the 

 course of development and subsequent growth. 



Sex of Parthenogenetically-developed Frogs. t — Jacques Loeb 

 refers to seven specimens of Rana pipiens over a year old, which 

 developed from unfertilized eggs. These eggs were pricked (after the 

 experiments of Guyer and Bataillon) with a needle that had been dipped 

 in blood. The young frogs were normal in growth and behaviour, and 

 a photograph is submitted of one which was killed at the age of ten 

 months. Some time ago Loeb and Bancroft inquired into the sex of 

 such parthenogenetically-developed tadpoles and frogs, but met with the 

 difficulty that ova persist for four months or so in the male gonads. 

 The ova were so few, however, that it seemed safe to conclude that the 

 young forms would have developed into normal males. Loeb has now 

 examined the testis of the ten months' old young frog and finds it 

 normal, with numerous spermatozoa. It would appear that in the frog 

 the male is heterozygous for sex, i.e. that the eggs are all alike and that 

 there are two kinds of spermatozoa, one with and one without a sex- 

 chromosome ; and that if a spermatozoon of the former type enters an 

 Qgg a female is produced. Another young frog, of similar origin, which 

 died at the age of thirteen months, proved to be a male. It had.swollen 

 first finders. 



*o^ 



Seminiferous Tubules of Birds.J — G. Carl Huber finds that these 

 are arranged in the form of a network, presenting a varying number of 

 anastomoses found at different levels in the gland substance. Teased 



* Journ. Anat., li. (1916) pp. 137-49 (5 figs.). 



+ Proc. Nat. Acad. Sci., ii. (1916) pp. 313-7 (2 Ggs.). 



X Anat. Kecord, li. (1916) pp. 177-80 (1 pi.). 



