ZOOLOGY AND EOTANT, MICROSCOPY, ETC. 33 



by the membrane which lines the pallial cavity and, therefore, exists 

 in Chilostomata as well as in Cyclostomata ; in the Lopliopoda, the 

 vestibule and the annular fold which forms it represent the 

 pallial chamber and the mantle respectively. The most striking 

 feature of the development is the fixation of the embryo by the oral 

 end. With this is connected the inversion of the mantle towards the 

 point of fixation, the inverse of what takes place in the Brachiopoda. 

 The fate of the chief parts of the larva is as follows : — The aboral 

 face forms the wall of the cell, or a considerable part of it, and also, 

 by invagination, the epithelial layer of the polypide. The ciliated 

 zone entirely disappears. Much of the oral face disappears, but 

 forms part of the wall of the cell, together with the rudiment of the 

 internal muscular layer. 



Arthropoda. 



o. Insecta. 



Olfactory Organs of Insects.* — The chief results of G. Hauser's 

 histological investigations into the structure of these organs may be 

 thus summed up : — 



In all Orthoptera, Pseudoneuroptera, Diptera, and Hymenoptera, 

 as well as in many Lepidoptera, Neuroptera, and Coleoptera, a strong 

 nerve arising from the cerebral ganglion passes into the antenna ; 

 there is a sensory terminal organ, formed by bacillar cells developed 

 from the hypodermis, with which the nerve-fibres are connected. 

 In addition to these parts there are supporting and accessory 

 organs formed by the pits or cones which are filled with fluid, and 

 which are invaginations or processes of the epidermis. If we select 

 the Orthopterous Calopterus italicus for a more detailed study, we 

 find that the antennae are setiform, but rather wider at their middle 

 than at the base ; they are made up of twenty-two joints, the surface 

 of which is divided by grooves into a number of small, somewhat 

 elevated areas, rhomboidal in form. On the basal and a few succeeding 

 joints stiff tactile setae may be detected ; on the eighth or ninth we 

 find, in addition to these setfe, rounded, irregularly shaped orifices, 

 covered over by a delicate membrane and surrounded by a chitinous 

 wall ; these may be arranged singly, by pairs or in groups, and as 

 many as fifty pits may be found in one joint ; within the pits we 

 find serous fluid. The bacillar cell already mentioned is connected 

 with a pretty strong nerve-fibre. Among the Coleoptera we find that 

 Melolontha vulgaris (male) has 39,000 of these pits, and the female 

 35,000 ; in Dytisms marginalis they are said to be very distinct. 



The functions of the organs were investigated by a series of ex- 

 periments. The antennae having been extirpated, the insects, which 

 had previously been tested in the presence of such highly odorous 

 bodies as turpentine, carbolic acid, and so on, were again tried, and 

 exhibited no repugnance at all in the presence of these compounds. 

 It was also found that when the antennae were removed the insects 

 did not rush to food. Observations on the value of the antennae to the 

 males in seeking out the females were not completely satisfactory. 



* Zeitschr. wiss. Zool., xxxiv. (1880) pp. 367-408 (3 pis.). 

 Ser, 2.— Vol. I. I) 



