ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 43 



Moina redirostris, a small clear spot situated at the superior pole, 

 enclosed in the vitellus, which he regards as a polar globule flattened 

 by the envelope of the ovum which is closely applied to the vitellus. 



On examining recently-laid ova of Asellus aquaticus, M. L. F. Hen- 

 neguy saw, in the tolerably wide space which separates the vitellus 

 from the chorion, two small transparent globules, containing a few 

 granules, and presenting all the characters of the polar globules, 

 observed in the ova of other animals. He also twice saw one of these 

 globules detach itself from the vitellus. In all the ova examined 

 these little bodies were nearly of the same diameter. In some ova 

 there were four of them, forming a group, and they were then smaller 

 than in the ova in which there were only two ; it is probable that in 

 this case the two globules had divided. These globules persist for 

 some time in the ovum, and only disappear when the vitellus is 

 already divided into about ten segments. The first segmentative 

 grooves forming simultaneously around nuclei which make their 

 appearance at the surface of the vitellus, the polar globules do not 

 here play any part in relation to the production of the first segmenta- 

 tive furrow, and cannot be regarded as directive corpuscles. Their 

 formation is very probably connected with the disappearance of the 

 germinal vesicle, as Fol and Hertwig have demonstrated in the case of 

 the Echinoderms ; but the opacity of the vitellus has not allowed the 

 author to see the germinal vesicle, or to witness its disappearance. 



Vermes. 



Development of the PolychaBtous Annelids,*— Some of the early 

 stages in Clymenella and Arenicola have lately been observed by Mr. 

 E. B. Wilson. 



The eggs are found in transparent gelatinous masses which, in the 

 case of Arenicola, may come to be five or six feet in length and two to 

 four inches in diameter. No polar globules were observed. At the 

 first cleavage the egg is divided into two unequal spherules; at 

 the second the smaller spherule is divided into two equal and the 

 larger into two unequal parts ; next, four much smaller cells separate 

 from the four blastomeres, and soon the micromeres alternate with 

 the macromeres ; the former now divjde more rapidly, and ultimately 

 grow over the macromeres, part of which do, however, as the writer 

 believes, go to form part of the epidermis. The remaining macro- 

 meres form the endoderm ; two larger derivates of the macromeres 

 apparently form the primary mesoblasts. The mouth arises on the 

 ventral surface, and nearly opposite the pole at which the first four 

 micromeres appeared. The anus is formed at the posterior end. The 

 egg-membrane is said to pass into the cuticle of the larva. During 

 segmentation, periods of activity alternate with periods of repose. The 

 larva is telotrochous, the setae develop from before backwards, and 

 those of the dorsal before those of the ventral ramus. The segmen- 

 tation appears to be very similar to that of the Oligochseta and 

 Discophora. 



* Amer. Journ. Sci., xx. (18S0) pp. 291-2 ; Ann. and Mag. Nat. Hist., vi. (1880) 

 pp. 407-8. 



