358 SUMMARY OF CURRENT RESEARCHES RELATING TO 



quence of this thickening the secondary follicular cavity is completely 

 filled by cells, and forms a mass between and from which the muscles 

 and the blood are derived ; it may, therefore, be looked upon as 

 analogous to the mesoderm, from which it is to be distinguished by 

 the fact that it takes no part in the formation of the heart. The 

 embryo, at this period, increases in length and approaches its definite 

 form. 



The preceding observations deal with what has been seen in Salpa 

 pinnata, and in concluding his account of the latest development of the 

 organs, Salen sky directs attention to the history of its nervous system, 

 which is important for the early connection which obtains between 

 the rudimentary nervous system and the enteric tract. 



The history of Salpa africana is not so fully dealt with as that 

 of S. pinnata, but an opportunity is taken to refer to the services 

 rendered by Barrois, and to point out the dificrences in the two sets of 

 observations. The important, or apparently important, distinction 

 between S. africana and S.pinnata lies in the presence of a body-cavity 

 in the former; this would seem to depend on the greater poverty of cells 

 in part of the mesoderm, and in the absence of that proliferation of the 

 cells of the wall of the follicle to which attention has already been 

 directed in speaking of S. pinnata. In other words, the embryos of 

 S. pinnata are provided with a body-cavity, but it is very early filled 

 up with cells. The paper concludes with a few words on the characters 

 of the placenta, and speaks in terms of approbation of Barrois' work 

 on this subject. 



Anatomy and Histology of Brachiopoda Testicardinia.* — J. F. 

 van Bemmelen, after an exhaustive survey of the work of preceding 

 students of this group, deals in detail with the various organs. 



Treating of the shell, he finds that the perforations in it do not 

 alter with age, and, since new canaliculi are not formed, it follows 

 that the shell of the Brachiopoda does not grow by intussusception, 

 but only at the margin. The so-called shell-papilla have often 

 been compared with the vascular outgrowths in the cellulose-mantle of 

 the Tunicata, but as the spaces in the former do not communicate with 

 the vessels in the mantle, it is obvious that no close comparison is 

 possible between the two sets of organs. The shell of the Brachiopoda 

 is only a cuticular structure, comparable to that of Annelids and 

 Arthropods, and is not of the same nature as that of the MoUusca, 

 which arises from a shell-gland. 



The proper body-wall is to be distinguished from the mantle ; the 

 ectoderm forms a single layer of epithelial cells which have large 

 nuclei, but are themselves relatively small. The layer of connective 

 tissue consists of a true supporting substance lying between 

 the ectoderm and the parietal mesoderm ; varying in thickness, 

 according to its relations to different organs, it has always a homoge- 

 neous structure with interspersed connective-tissue cells. Distinct 

 bands of tissue are to be made out in some genera, but they all seem 

 to be nothing more than differentiations of the homogeneous supporting 



* Jen. Zeitechr. f. Naturwiss., ix. (1882) pp. 88-161 (5 pis.). 



