644 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Development of Eoperipatus weldoni.*— Bichard Evans finds that 

 in this form the ova originate in the manner called exogenous by Willey, 

 and not endogenously as in the species of the genus Peripaius. There 

 is reason to believe that the process of overgrowth of the yolk takes 

 place from the future ventral surface towards the dorsal, as in so many 

 Arthropods. In early embryos a remarkable structure occurs in front 

 of the somite usually described as the first, which the author interprets 

 us a vestigial cerebral somite. In the development of the coelom, 

 Eoperipatus closely agrees with Pcripatus capensis, as described by 

 Sedgwick. The author finds that the germinal nuclei originate in the 

 mesoderm, and not in the endoderm as described by Sedgwick. The 

 male accessory glands arc also in part mesodermal, and the cavity of 

 their inner moiety coelomic. In consequence, the salivary glands, the 

 renal organs, the genital ducts, and the male accessory organs, must all be 

 regarded as homologous structures, derived from the mesoblastic somites, 

 and communicating with the exterior by means of a short invagination of 

 the ectoderm. As in P. capensis, the eye develops from the brain. 



Peripatopsis blainvillei.-f— E. L. Bouvier has pursued his observa- 

 tions on this interesting American form, and finds that, in regard to the 

 structure of the reproductive organs and the development, it seems to 

 be transitional between the other American forms belonging to the 

 genus- Peripatw s. str. and the South African me-nbers of the genus 

 Peripatopsis. A comparison of the eggs of the different genera shows 

 that the characters of these arc exceedingly variable in the group, and 

 cannot be relied upon in establishing generic distinctions. The eggs 

 are small and without the " embryonic annex " in P. blainvillei, and a 

 comparison with other American forms leads the author to conclude 

 that the existence of this organ in a highly differentiated condition is an 

 archaic character, and not a mark of specialisation as has been supposed. 

 He believes that the ancestral forms were viviparous, and that as an 

 adaptation to this the embryonic annexes became developed, and formed 

 the " placenta." In the more specialised forms the eggs increased in 

 size as yolk was developed, and the placenta became functionlcss as the 

 oviparous habit was acquired. The primitive viviparous habit was 

 rendered necessary when the aquatic ancestors first became terrestrial. 



S. Arachnida. 



Genus Tetranychus.J— Dr. Eeinold v. Hanstein, in the course of a 

 paper on this genus of mites, defines T. althsese, contrasting it with T. 

 telarius, and, by following the life-history of the latter, definitely dis- 

 proves the statement sometimes made that Leptus autumnalis is the larval 

 form. In both the species mentioned there is only one stigma, placed 

 in the middle line beneath the epistomc. It communicates both with a 

 thick- walled tracheal tube which divides into two ventral branches, and 

 also with two anterior branches. In the life-history there occurs a six- 

 legged larval stage, and two eight-legged nymph stages, three immov- 

 able chrysalis-stages being intercalated. No apoderma formation occurs 



* Quart. Joura. Micr. Sci.. xlv. (1901) pp. 41-8S (5 pis.). 



t Comptes Bendus, exxxiii. (1901) pp. f>18-21. 



X Zeitschr. wiss. Zool., Ixx. (1901) pp. 08-108 (1 pi.). 



