600 SUMMARY OF CUERENT RESEARCHES RELATING TO 



duck, rat, cat, etc.) tubuli arise as buds from the floor of the pouch, 

 and these may be constricted off. By a similar budding, tubules may 

 arise on the dorsal sac (fowl, rabbit), which are referable to the paren- 

 chyma of the pineal organ. 



To begin with, the organ is epithelial. This is modified into 

 neuroglia. In some cases (e.g. canary) the tubules may remain hollow ; 

 in other cases (e.g. fowl and rabbit) the lumen is more or less com- 

 pletely obliterated. A lumen may appear secondarily, as- in the ox. 

 Around the lumen, whether primary or secondary, the cells become 

 ependym-like. Otherwise, the parenchyma cells have the character of 

 astrocytes. The parenchyma is invaded by connective-tissue septa with 

 blood-vessels. Apart from fine nerve-threads accompanying the vessels, 

 there was no trace of nerve-cells or nerve-fibres. No muscle-cells were seen. 



Spermatogenesis in Hybrid Pigeons.* — Geoffrey Smith has studied 

 the spermatozoa and spermatogenesis in normal male pigeons and doves, 

 and in three male hybrids produced by the mating of a male pigeon 

 with a female domestic dove. The ripe spermatozoa of the hybrids 

 showed in certain cases structural abnormalities, and were on an average 

 twice as large as the normal spermatozoa of either parental type. 



The first maturation or reduction division in the hybrids is abnormal, 

 in that the chromosomes do not enter into the normal synapse to produce 

 eight synaptic or bivalent chromosomes, but they are scattered as irregu- 

 lar cliromatic masses of unequal size on the mitotic spindle, and are 

 irregularly distributed to the opposite poles of the spindle. 



The second maturation division in the hybrids is almost entirely 

 suppressed, the secondary spermatocytes proceeding without further 

 division to form spermatids and spermatozoa of twice the normal size. 

 Many of these spermatozoa are structurally normal, apart from their 

 double size, while others are abnormally twisted or beaded. All were 

 probably impotent, these hybrids and all others of a similar kind being 

 invariably sterile. The explanation of the sterility of such hybrids is 

 found, in accordance with Guyer's idea, to reside in the disturbance of 

 the synaptic division during maturation, this disturbance being due to 

 the incapability of the chromosomes derived from the specifically different 

 parents to fuse to form the normal synapses. 



Development of Thoracic Duct in Turtles.f — Frank A. Stromsten 

 has studied this in the loggerhead turtle. According to Ranvier and 

 Sabin, lymphatics are modified veins ; according to Huntingdon and 

 McClure lymphatic channels arise from the confluence of spaces inde- 

 pendent of the venous system, though closely associated with them. 

 Stromsten establishes the presence of independent lymph spaces which 

 lie beyond the field of the injected vessels, and finds that these lymph 

 spaces by fusion aid in the formation of a peri-aortic lymphatic plexus, 

 which is afterwards directly transformed into the prevertebral (thoracic) 

 duct. The formation of the peri-aortic lymphatic plexus in the logger-. 

 head turtle is always preceded by a vacuolation of the mesenchyme in 



* Quart. Journ. Micr. Sci., Iviii. (1912) pp. 159-70 (1 pi.). 

 t Anat. Record, vi. (1912) pp. 343-56 (8 figs.). 



