ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 39 



All except the last are stemmata. Scutigera ( = Cermatia) has com- 

 pound eyes of a very anomalous type, in no wise resembling that of 

 Insects and Crustaceans. Without copying his figures, we could not 

 usefully abbreviate Grenacher's descriptions. 



Thus far it may be concluded that the eyes of Chilopods are more 

 polymorphic and more complex than those of Chilognaths. Sograff 

 says that the eyes of Lithobius and Scolopendra are quite like the 

 eyes of coleopterous larv^, as well as of spiders. They cannot, 

 however, be thus compared with both of these, which Grenacher 

 has shown to represent the two principal types of stemmata, respec- 

 tively. The eyes of Julus and Glorneris, but not of Lithobius, have 

 their soft parts disposed in one layer, and so far may be likened to 

 the (monoderic) eyes of the young Dytiscus, or of the Acilius-l&VYa. 

 In the Scolopendridge we are met by this difficulty — that the eyes of 

 the same species, at different stages, may show two different struc- 

 tures ; nor can it yet be said which of these two be the primitive. 



Physiologically, the simple eyes of at least some Myriapods must 

 be very unlike the ordinary stemmata of spiders or insects. These 

 are true perceiving organs. In Myriapods, on the other hand, each 

 stemma has its retinal elements, or their representatives, so disposed 

 in regard to the axis of the cornea-lens, and therefore to the incident 

 rays of light, that it seems very doubtful whether such eyes can do 

 more than distinguish between degrees of light and darkness. Grena- 

 cher admits that this is a rather paradoxical result, when we consider 

 the apparent waste of means involved [but is not in contradiction to 

 the derivative hypothesis]. There is yet need of much exact work in 

 this wide field of inquiry. 



The eye of Limidiis, already roughly compared by Grenacher with 

 the Myriapod-eye, is now more closely affined to that of Julus or 

 Glorneris, since it appears to be one-layered. 



y. Araclinida. 



Poison-glands of Spiders.* — It has long been known that spiders 

 possess a pair of glands, presumed to be venomous, opening by long 

 excretory ducts at the free ends of the cheliceres. Dr. J. MacLeod 

 has examined these glands in several spiders, and gives details of their 

 minute structure. 



The body of the gland consists of two layers, muscular and secre- 

 tory. The muscles constitute a uniform stratum, resolvable into 

 spiral bands, which are closely set and quite flush with one another 

 because of their very regular thickness. Each muscular fibre has a 

 pointed end, by which it dovetails gradually with its neighbour. 

 Transverse striae, often difficult of detection, seem always to be pre- 

 sent. Numerous nuclei are deeply sunk in the muscular substance ; 

 these nuclei are disposed in longitudinal rows, of which as many as 

 six in parallel lines have been counted in a single fibre. Eegularly 

 prismatic fibres, showing four sides in cross-sections, were seen in 

 certain species. 



An outer envelope of thin connective tissue, with nuclei here and 

 * Arch, de Biol., i. (18S0) pp. 573-82 (1 pi.). 



