660 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



nerve in a median direction. By division, they yield a syncytial cellular 

 strand, which extends from the spinal nerve towards the aorta, and in 

 this way a primary cellular ramus communicans arises. This divides up 

 into a greater number of columnar cell-masses, which are connected by 

 cell processes with each other. These cell-masses, originating from the 

 neurocytes of the spinal nerves, form the primordium of the sympathetic 

 sheath. Embryonal neurocytes may take a share in the formation of 

 peripheral spinal and sympathetic nerve-fibres, in the development 

 of peripheral ganglion-cells, in the regeneration of peripheral nerve- 

 fibres, and in the pathological re-formation of ganglion-cells. 



Development of the TrachinidaB.* — J. Boeke, following up an 

 earlier account of the eggs of the two species of TracJiinus, T. vipera 

 and T. draco, inhabiting the North Sea, describes the larval and post- 

 larval stages of these two forms, of which he has been able to procure 

 an unbroken series. The two species differ greatly even in the egg, 

 and T. draco, the Greater Weevil, may be known from the Lesser in the 

 larval stages by the relatively greater size of the head and the upturned 

 mouth. Sijines are developed early in both species, and the adult 

 colours begin to appear when the fish reach a length of 16-17 mm. 



Parturition of White Rat.f — E. Brumpt gives an account of this 

 process. The " presentation " is variable, it may be " breech " or head. 

 The umbilical cord does not break spontaneously, and if it breaks 

 accidentally it is at some distance from the umbiHcus. Certain foetuses 

 are expelled along with the placenta and their annexes. In others the 

 cord breaks, or is broken by the mother, and the birth is a separate 

 operation. In one case where the number of young was 10, 6 were in 

 the right uterus and 4 in the left. They were expelled irregularly ; the 

 right horn probably held foetuses 1, 3, 5, 8, 9, 10, and the left 2, 4, 6, 

 and 7. 



Structure and Development of Sperms in Rana.f — Ivar Broman 

 gives a very detailed account of the structure of the mature sperms in 

 several species, and traces the development in R.fusca. In one point 

 the course of development in R.fusca deviates from that of all others 

 investigated whose spermatids possess a centriole ring which has arisen 

 in the interior of the cell. The centriole ring which has arisen from 

 the distal centriole in this species disappears mainlj in loco without 

 having either entirely or partly migrated beforehand caudalwards. The 

 significance of the centriole ring has not been made out ; it is suggested 

 that it may be a part of the centriole which has arisen by excessive 

 growth, and which is thrown off as useless or injurious to later function. 



Tooth-development in Ornithorhynchus.§ — J. T, Wilson and J. P. 

 Hill describe the conditions of tooth development in two foetal Orni- 

 thorhynchi of different stages. The facts set forth seem to establish 

 the existence in Ornithorhynchus of teeth belonging to at least two 



* Tidschr. Nederland. Vereen., 2nd series (April 1907) pp. 245-54 (1 pi.). 



t Bull. Soc. Zool. France, xxxii. (1907) pp. 50-2. 



X Arch. Mikr. Anat., Ixx. (1907) pp. 330-59 (2 pis. and 4 figs.). 



§ Quart. Journ. Micr. Sci., li. (1907) pp. 137-65 (3 pis.). 



