574 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



(2) In 1880 he "implicitly" stated the distinction of the three Arthropod 

 series — Crustacea ; Gigantostraca, Arachnoidea ; Myriopoda-Insecta. 



(3) His views as to the relation of Limulus to the Arachnoidea are quite 

 different from those of Prof. Eay Lankester. 



(4) The reference of the Mites to retrograde Arachnoidea, which is sup- 

 ported by the discovery of the rudimentary heart, has been for many years 

 supported on other grounds than those of Lankester. 



(6) The hypothesis of the " adaptational shifting of the oral aperture " 

 is perfectly untenable. 



(6) And it has nothing in common with the opinion, founded on the 

 conditions of innervation, that the second pair of antennas of the Crustacea 

 represents the foremost truncal members, while the first pair, like the 

 antennae of Insecta and Myriopoda, belong to the praestomial part of the 

 head. 



a. Insecta. 



Some interesting processes in the formation of Insects' Ova.* — Dr. 



E. Korschelt, as a first of a series of accounts of interesting processes in 

 the formation of the ova of insects, gives a description of an abnormal mode 

 of development in the origin of the egg-rays of Banatra linearis. This 

 may be taken as a supplement to his description of the peculiar mode of 

 formation of the chitin of the so-called egg- rays of Nepa cinerea. In that 

 form the egg has at its upper pole seven filamentous appendages — the egg- 

 rays — which serve to bring air to the submerged egg. For this object they 

 are porous at their tip and internally, and this porous substance is connected 

 with a similarly porous layer in the egg-shell. The rays of Nepa do not arise 

 in the usual way in which chitin is formed, for they are not cuticular products 

 excreted by the epithelial cells, but are developed within specially modified 

 cells. The allied Banatra linearis has two rays only, but these are longer 

 than those of Nepa, with which they agree in internal structure. While the 

 egg-shell proper is developed in the typical mode of chitin formation, the 

 rays are, as in Nepa, formed within specially modified cells. The epithelial 

 tissue thickens in the upper lateral wall of the younger ovarian chambers. 

 Owing to this increase in size, the upper wall gets a ridge-like thickening. 

 In the youngest chambers this consists of similar cells, but in those that 

 are a little older the nuclei begin to increase in number. Among the 

 epithelial nuclei of the ordinary size there appear some larger ones, which 

 are already so far altered that they appear to be filled with a number of 

 small chromatin particles. In a more advanced stage the increase in size 

 becomes more marked, and this goes on with age. Plasmatic spaces appear 

 around the larger nuclei, which thus look as though they were surrounded 

 by a cell-body. The increase in the size of the nuclei is accompanied by a 

 multiplication of the cells, and the thickening, within which the rays are 

 to be formed later on, is very different from the rest of the cell-wall. The 

 next process which becomes noticeable is that four of the larger nuclei 

 arrange themselves by pairs, and become almost completely attached to one 

 another. Henceforward these are the cells which grow most, all the other 

 nuclei being left far behind. The histological structure which contains the 

 two nuclei may be well called the double cell. In Banatra it is not so 

 early or so strikingly characterized as in Nepa. The chitin of the egg-rays is 

 formed within the double cells between the nuclei, the cell-plasma which lies 

 there being directly converted into the chitinous substance ; the ray is first 

 formed at its base, and begins to grow considerably. The cuticula-like layer 



* Zeitschr. f. Wiss. Zool., xlv. (1887) pp. 327-97 (2 pis.). 



