ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 961 



Arthropoda. 



Maturation of the Arthropod Ovum.* — Herr F. Stuhlmarm con- 

 tributes a welcome investigation of the phenomena of maturation in the 

 but little known Arthropod ova. 



Some of the uniform nuclei of the germinal layer are seen to 

 differentiate towards ova. At an early stage they can be detected in 

 stained preparations. They exhibit a central and a number of peri- 

 j>heral chromatin bodies, but the latter disappear. No passage of 

 chromatin bodies from the nucleus was observed. At an early stage 

 the germinal vesicle, formed as above, wanders to the periphery, 

 seems to get flattened up against the follicular epithelium, and very 

 often loses its nucleolus. In many insect ova a number of balls re- 

 sembling the nucleus in their constitution, seemed to be extruded 

 from the germiual vesicle on the side next the follicular epithelium. 



The occurrence of polar globules is discussed ; their apparent 

 absence in large ova rich in yolk ; their presence in small ova, like 

 those of Moina and Polyphemus. The expulsion of the above globules 

 of maturation occurs at a very early stage, before the egg has attained 

 half its size. After their expulsion the germinal vesicle is drawn 

 inwards and eludes observation. In Aphides and Cecidomyia larvas 

 it remains visible. It seems to become amoeboid in the large ova 

 richly equipped with yolk, but is probably in most cases distributed 

 in the protoplasm. 



As to the so-called yolk-nuclei, they do not, according to Stuhl- 

 mann, arise from the germinal vesicle. They appear near the germi- 

 nal vesicle and move to the periphery or to the superior pole, or re- 

 main diffuse. They may unite further into a single large mass at the 

 posterior pole. They are simply yolk-concretions of a nutritive 

 character, afterwards absorbed. 



Terminations of Motor Nerves in Arthropod Muscle.| — As the 

 result of his investigation of the terminations of the motor nerves in 

 the striped muscle of Arthropods, Siguor U. Gabbi comes to the 

 following general conclusions : — 



1. In Musca, Libellula, Oryetes, Silpha, &c, the primitive muscle- 

 bundle presents a close structural resemblance to the muscular bundle 

 in Vertebrates. 



2. In the Arthropods mentioned the ensheathing envelope of the 

 motor nerve, which enters into close relations with the primitive 

 muscle-bundle, is continued into the sarcolemma, which forms the 

 investment of the so-called elevation of Doyere. 



3. The axial cylinder, penetrating the apex of the elevation of 

 Doyere, increases slightly and divides, except in Musca, into two 

 branches ending at the base of the cone. In Musca the two primitive 

 branches undergo a further bifurcation. In all the Arthropods 

 examined the motor termination is situated below the sarcolemma. 



* Biol. Centralbl., vi. (18S6) pp. 397-402. Ber. Freib. Naturf. Ges., i. 

 (1886). 



t Bull. Soc. En torn. Ital., xviii. (188G) pp. 310-32 (2 pis.). 

 Ser. 2.— Vol. VI. 3 R 



