40 SUMMABY OF CURRENT RESEARCHES RELATING TO 



SUMMAEY 



OF CURRENT RESEARCHES RELATING TO 



ZOOLOaY AND BOTANY 



{principally Invertehrata and Gryptogamia), 



MICEOSCOPY, &c., 



INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOAVS AND OTHERS/ 



ZOOLOGY. 

 A. VERTEBRATA: — Embryology, Histology, and General. 



a. Embryology, f 



The Archistome Theory.^ — Mr. J. A. Eyder gives a brief sketch 

 of a new theory of development. 



He expands Hackel's gastraea theory in the light of more recent 

 research, and agrees with Sedgwick's theory on the " origin of meta- 

 meric segmentation," except as to the homology of the mouth and 

 anus of the vertebrates with those structures of the invertebrates. 

 He mainly concerns himself with the origin of the appendages. The 

 medullary plate has been formed by the concrescence of the lips of an 

 elongated blastopore in all forms. The mouth and anus of vertebrates 

 are new structures. 



The " archistome " is the elongated mouth of the larvae of 

 Bilateralia, or the whole area embraced by an unpaired median neural 

 plate, or by a pair of neural plates. This archistome extends in 

 vertebrates from the pineal gland along the whole length of the body, 

 through the " secondary blastopore," and through the primitive streak 

 to the point of closure of the " yolk blastopore." 



If an actinozoon is elongated along the long axis of the mouth, 

 the tentacles will become arranged in pairs on each side of the archi- 

 stome ; each has a portion of a gut-pouch continued into them ; the 

 telson and labrum may be supposed to be derived from the opposite 

 extremities of the series of tentacles. The biramose appendages of 

 Crustacea are derived from an actinozoon with two rov\^s of tentacles 

 or " archipodia," by the fusion of the bases of the tentacles of the 



* The Society are not intended to be denoted by the editorial " we," and they 

 do not hold themselves responsible for tlie views of the authors of the papers 

 noted, nor for any claim to novelty or otherwise made by them. The object of 

 this part of the Journal is to present a summary of the papers as actuallij published, 

 and to describe and illustrate Instruments, Apparatus, &c., which are either new 

 or have not been previously described in this country. 



t This section includes not only papers relating to Embryology properly so 

 called, but also those dealing with processes of Evolution, Development, and 

 Ecproduction, and with allied subjects. 



% Amer. Natural., xix. (1885) pp. 1115-21. 



