622 SUMMARY OF CURRENT RESEARCHES RELATING TO 



In the course of tlie develoj)ment of the placenta the cavities of the 

 crypts lined by much altered uterine epithelium may be filled with 

 maternal blood ; this is due to the pre^^ence in the crypts of holes with 

 no proper walls, which traverse the ej)iblastic mass in such a way as to 

 establish communications between the lacunar blood-system of the 

 placenta and the ej)itLelial crypts. This arrangement allows of the 

 presence of the maternal blood between the epiblast and the sui-face of 

 the mucous membrane of the uterus. 



Structure of Graafian Follicle in Didelphys.* — Mr. F. E. Beddard 

 gives an account of the Graafian follicle in the Opossum, which agrees 

 more closely with that of PJiascolarctos than with that of Phalangista ; 

 that of the last-named Marsupial seems to the author to nearly represent 

 the hypothetical intermediate condition between the Monotremata and 

 the higher Mammalia. 



Early Development of Lepidosteus osseus.f — Dr. J. Beard gives an 

 outline of the development of Lepidosteus during the first three weeks 

 of its life. The investigation of that of the first four days is very 

 difficult ; for the yolk outside the embryo gives rises to technical 

 difficulties, while that which fills all the cells renders everything 

 blurred and indistinct. As to the egg the author has little to add to 

 the description given by Balfour and Parker. The blastopore closes on 

 the second day, and at no time is there a neurenteric canal ; the mesoderm 

 arises very early and before the closure of the blastopore. The epiblast 

 is very early divided into two layers, the outer of which takes no share 

 in the formation of organs, and may be, perhaps, compared to the skin 

 of a larval Annelid ; the inner layer may be spoken of as the formative 

 epiblast. In the central nervous system the transient giant ganglion- 

 cells may be distinguished from the ciliated groove which forms the 

 floor of the primitive central canal. The roof of the fore-brain is very 

 thin both in embryo and adult ; it is non-nervous and epithelial in 

 character, as in Marsipobranchs, Teleostei, and other Ganoids. 

 Behind the anus the spinal cord is for some time solid. 



The larval suckers are developed very early, in the form of a number 

 of closed spherical sacs, a part of the wall of which is thin and soon 

 ruptured. The functional suckers are composed of two sorts of cells — 

 long, glandular cells with hyaline, slightly granular contents and a 

 nucleus lying uear the inner end of the cell, and supporting cells with 

 the nucleus in the middle of the cell. 



The first branchial cleft is formed long before the others and before 

 hatching ; the pneumatocoele arises at a very early period and long 

 before hatching ; it is a fold of the neural median hypoblast and grows 

 backward in length, apart from connection with the alimentary canal. 

 The somites, which are at first solid, are long and narrow ; the inner 

 wall of the somites gives rise to muscle, and most of the outer wall is 

 converted into pigmented connective tissue. The pronephros is formed 

 as a solid evagination of the mesoblast ; it probably fuses with the 

 epiblast ; at any rate a solid segmental duct is formed, probably from the 

 inner epiblast layer. Three funnels seem, as a rule, to be formed on 

 each side of the body, but the most posterior of them disappear, the 

 others persisting throughout the larval period. 



In conclusion, the author calls attention to a transient and larval 



* rroc.K. Phys. Soc. Edinb., ix. (1SS8) pp. 407-12. 

 t Fioc. Eoy. Soc. Lond., xlvi. (1SS9) pp. 108-118. 



