40 SUMMARY OF CURRENT RESEARCHES RELATING TO 



ectoderm ; but the food-canal, with the exception of a small buccal region, 

 has an endodermic origin. There is no special mesoderm primordium, nor 

 do the regeneration-cells arrange themselves in special masses for the. 

 different organs. Two periods can be distinguished in the process of 

 regeneration : — the first is the organogenetic period, when the foundation 

 of the organs is laid down ; and the second the growth period, when the 

 new organs acquire their normal relative size. The nervous system is 

 the first structure to be regenerated in all cases, and of its parts the 

 brain developes first, then the gullet ring, and finally the ventral chain. 

 The first indication of segmentation in the regenerated region occurs in 

 the ventral nerve-chain, which divides up into metameric ganglia. Later 

 the dissepiments are formed, and finally the bristles appear and the seg- 

 mentation becomes visible externally. 



The author's observations were made on worms artificially mutilated, 

 but he finds that Lumbriculus exhibits transverse division under normal 

 conditions as a form of asexual reproduction. He distinguishes gene- 

 rally artificial regeneration as reparation, from the true regeneration 

 which follows on normal asexual reproduction, but notes that in Lum- 

 hriculus there is virtually no distinction between the two processes. 

 Except for the extreme head and the tail, the power of regeneration is 

 very great at all j^arts of the body. 



Egg of Allolobophora foetida.*— Miss K. Foot and E. C. Strobell 

 publish a series of photomicrographs of this egg, which they have taken in 

 order to illustrate the following points : — (1) the effect on the cytoplasm 

 of the different fixatives in common use ; (2) the characters of the fer- 

 tilisation cone ; (3) the position of the middle piece in the male aster ; 

 (4) the origin of the sperm-granules ; (5) the early stages in the de- 

 velopment of the pronuclei ; (6) the presence of osmophile granules in 

 the nucleoli of the germinal vesicles. The photographs have been taken 

 at two magnifications, 660 and 950, and the authors believe that they 

 furnish objective proof of some of Miss Foot's previous conclusions, e.g. 

 in regard to the cytoplasmic origin of the centrosome of the male aster. 

 The paper is the first of a series of illustrated studies in which the 

 authors hope to treat the first point especially in detail. 



Structure of Leech Somite.f — Mr. J. Percy Moore notes that in his 

 recent paper | ona new biannulate leech, he made no mention of Oka's § 

 leech (Ozobranchus mendiesi?^), as the description had escaped his notice. 

 In the present communication he points out the resemblances and dif- 

 ferences between his own and Oka's biannulate form. The resemblances 

 he regards as striking, the somite in each case consisting of a large and 

 a small annulus. Further, he believes that they are such as to confirm 

 his view that the large annulus is the equivalent of the neural annulus 

 plus its predecessor in Pontobdella, and therefore that the neural annulus 

 is ruorjmologically the middle ring of the 3-annulate leech somite. 



Protonephridia of Leeches.|j — Boris Sukatschoff has studied these 

 structures in embryos of Nephelis vulgaris and Aulastomum gido, with 

 special reference to Bergh's views as to their relation to those of Poly- 



* Journ. Morph., xvi. (1900) pp. 001-18 (3 pis.). 

 f Zool. Anzeig., xxiii. (1900) pp. 474-7 (1 fig.). 



Cf. tins Journal, 1900, p. 585. § Zool. Mag., vii. (1895) pp. 1-7. 



Zeitschr. wiss. Zool., lxvii. (1900) pp. (318-39 (2 pis. and 3 figs.). 



