(ill SUMMARY OF CURRENT RESEARCHES RELATING TO 



able for communicating with two lateral canals; these canals pass 

 forwards for about 6 or 7 nun. ; this is an arrangement which has not 

 been described in any other leech. 



The cervical part of the nervous system is reduced to a com- 

 missure ; and the epidermis is segmented in mctameres corresponding 

 to those of the nervous system. There are five pairs of testicles, and 

 two saccular ovaries. Glands comparable in form and position to what 

 arc ordinarily called salivary glands are to be found in the anterior 

 region of the body, between its walls and the proboscis. 



' Challenger ' Polychseta.* — An elaborate report on the Polychaata 

 collected during the voyage of II M.S. 'Challenger' has been pub- 

 lished by Prof. W. C. M'Intosh; the scries is described as being 

 extensive; no representatives of new families were found, but there 

 are 220 new species. In addition to the technical descriptions of 

 the forms, whether old or new, there are accounts of the eyes of the 

 AlcippidsB and Phyllodocidre by Dr. E. Marcus Gunn. The report 

 is indispensable to all workers on Annelids. 



Embryology of the Nemertinea.f — Prof. A. A. W. Hubrecht here 

 gives the English reader an account of his observations on the develop- 

 ment of Linens ohscurus, which were published last year in Dutch. J 

 Four discs, and subsequently a fifth, are formed by the epiblast ; the 

 former are due to the cubical cpiblast-cells dividing lengthways, 

 becoming overcapped by the surrounding epiblast and soon completely 

 enclosed within it. The fifth disc appears thus ; in the aboral region 

 of the epiblast the epiblast-cells are very distinctly delaminated, and a 

 double layer is formed which finally separates ; all the five discs are 

 one cell-layer thick, and they increase in size by continued division of 

 the constituent cells ; finally they meet along their edges ; they then 

 unite and form the continuous coat of secondary integument, outside 

 of which the primary epiblast is very soon cast off. Only at first is 

 the hypoblast a distinct unicellular layer ; later on its walls become 

 less distinct ; by budding mesoblast-cells are developed, which perform 

 amoeboid movements in the blastoccel into which they escape ; some 

 of them arise from the epiblast and some from the hypoblast, and 

 there is no definite localization of this process. It was noted that 

 the chromatic nuclear substance of the primary epiblast diminishes 

 near the time when it is going to be cast off; this decrease in the 

 significance of the primary epiblast as a formative element becomes 

 more and more marked as the young larva within it increases in size. 

 Prof. Hubrecht is of opinion that the primary epiblast is not dis- 

 integrated, but that the greater part of it is carried off by the mesoblast 

 cells or plays a further part in the formation of the larva. No portion 

 of the central nervous system of Linens takes its origin from either 

 primary or secondary epiblast, but the whole nervous system is of 

 mesoblastic origin. At first the archenteron communicates with the 



* Eeports of the voyage of H.M.S. 'Challenger,' xii. (1S85), xi. and 554 pp. 

 and 94 pis. 



t Quart. Joum. Micr. Scl, xxvi. (18S6) pp. 417-4S (1 pi.). 

 X 4to, Utrecht, 1885. 



