ZOOLOGY AND BOTANY, MICKOSCOPV, ETC. 451 



are the annular fibres ; they are connected by connective threads, con- 

 nective fibres, cleft fibres, and fork branches. The annular fibres work 

 in contraction in antagonism to their longitudinal connexions. The 

 connective threads and the various membranes show some elasticity, but 

 are not active in the contraction of the tubules. 



Influence of External Conditions on Nuclear Division in Cyclops.* 



Alfred Tobias has experimented chiefly with the eggs of Cyclops viridis, 

 and has been able to study the effect of altered temperature as such. 

 Increased temperature produces disruptive changes in oviducal eggs and 

 premature dicentric movement of the spindle, but has especially this 

 effect that the chromosome pairs in their biserial arrangement tend to 

 separate from one another, each pair by itself representing an idiomere- 

 like structure. 



In the maturation-divisions these bodies retain their independence, 

 they migrate to the periphery, and may even show separate maturation- 

 divisions. The chromosomes of the female pronucleus do not form a 

 unified single nucleus, but the idiomeres remain independent. There 

 may be multipolar maturation-divisions. Even in fertilization the 

 idiomeres tend to remain independent ; each may show a typical growth- 

 stage and prophase-stage. When the eggs are restored to normal tem- 

 perature, they may show several typical pseudo-amitoses. It should be 

 noted that clumps of ova separated from the mother Cyclops can 

 develop quite normally. 



Orientation in Crustaceans.f — W. von Buddenbrock has made 

 numerous experiments with swimming Crustaceans. There are a few, 

 like Lysmata seticaudata, which do not steer at all. There are some, 

 like Penseus, that depend on their statocysts. There are others, like 

 Phronima and larval Decapods, which depend solely on their light-reflex. 

 There are others, like Squilla mantis, which depend on their light- 

 reflex (associated with the eyes) and on a general position-reflex which 

 does not seem to be associated with any special sense-organ. In many 

 cases, such as Mysidoe and shrimps, there is a combination of light-reflex 

 (the dorsal surface turned to the light), the gravitational reflex (the 

 ventral surface turned to the centre of the earth), and the general 

 position-reflex. 



Annulata. 



Remarkable Epizoic Oligochgete.J — H. A. Baylis describes Aspido- 

 drilus kelsalli g. et sp. n., specimens of which were found by Major 

 Kelsall living as ; ' external parasites " on a large earthworm in Sierra 

 Leone. As the food-canal contained earth and vegetable debris, they 

 are probably commensals, not parasites. They were 5 mm. in length. 

 The posterior half of the body was flattened and expanded into an oval 

 disk bearing numerous transverse rows of ventral setae. Each of the 

 anterior segments bears two pairs of short straight setaj. The clitellum 



* Arch. Mikr. Anat., lxxxiv. (1914) lte Abt., pp. 369-429 (1 pi. and 53 figs.). 

 t Zool. Jahrb. Abth. Allg. Zool.,xxxiv. (1914) pp. 479-514 (5 figs.). 

 % Ann. Nat. Hist., xiv. (1914) pp. 145-51 (2 figs.). 



2 h 2 



