184 SELECTED NOTES. 



Haltere of Sericomyia borealis. — An examination of the haltere 

 above the spiracle on this slide, with a Zeiss' |-inch apochromatic, 

 shows its head to be trumpet-shaped, not globular, the trumpet 

 part being apparently continuous, with a long tube leading to the 

 special sense-organs below. Of course, the head may have been 

 globular and have become conical by shrinkage, but I do not 

 think so. Wm. Gifford. 



EXPLANATION OF PLATE IX. 



Fig. 1. — Section of Pulvillus of Sarcophaga carnaria. * jj.io., Posterior 

 wall ; s.t., Semi-tubes ; g., Glands ; /?., Fine hairs. 

 ,, 2. — One facette of Eye. c, Cornea; p., Pseudocone ; p.c. , Pig- 

 ment cell; n.p., Nuclei of Pseudocone; ?/.r.. Nucleus of 

 Retmula ; v., Retinula ; ^7;., Rhabdom ; t.v., Tracheal vesicle ; 

 6.C., Basal pigment cell ; t.f., Terminal fibres. 



,, 3. — Vertical Section through Head of Blow-Fly. e., Compound 

 eyes ; /.s. , Frontal sac ; p.h., Base of Proboscis retracted. 



,, 4. — Longitudinal section of third joint of Antennae of Blow-fly. 

 e.d.. Epidermis ; e})., Epithelium ; n., Nerve ; s.h., Sensitive 

 hairs ; ol., Olfactory organs. 



,, 5. — Section of Globe of Haltere of 8arcop>liaga carnaria. i., 

 Invagination ; c.t., Connective Tissue ; </., Glands. 



Additional Notes. 



Peronospora infestans (PI. XL) {Phytophthira of De Bary) 

 belongs to Oosporece, a group of Thallophytes distinguished by 

 their organs of reproduction — peculiar large cells called oogonia or 

 resting spores. P. infestans is remarkable for possessing two 

 modes of reproduction — first, a sexual one by oogonia and anthe- 

 ridia ; second, an a-sexual one by gonidia or buds (compare 

 Marchantia polyi?iorpha among the Hepaticae). The drawings on 

 Plate XL are partly copied from Sach's Text-book of Botany^ which 

 illustrates the life-history of this plant. 



In July or August it is first observed forming yellow spots on 

 the leaves of the potato, which then turn brown and wither. The 

 underside alone of the leaves is at first affected, as the stomata 

 there afford an easy mode of entrance to the germinating mycelia 

 of the fungus. In Fig. 2, Z, this is seen. The mycelia put forth 

 haustoria. Fig. 2, into the protoplasm of the cells to suck up 

 the sap, and the withering of the plant is caused by the fungus 



