742 SUMMARY OF CURRENT RESEARCHES RELATING TO 



degenerated placenta serves as food for the developing polypide. If tlie 

 planula of Alcyonella be compared with the annelid larva, the two folds may 

 perhaps be regarded as two metamorphosed ciliary bands. 



Characters of the Genus Lophopus.* — Mr, S. 0. Eidley points out the 

 unnatural characters by which genera and species of Phylactolsematous 

 Polyzoa are distinguished: as exampled in the separation of Alcyonella and 

 Plumatella, which differ from one another chiefly in the " manner of con- 

 nection between the tubes of the colony." He gives AUman's diagnosis of 

 Lophopus, as well as JuUien's addendum to it, but the discovery of a new 

 species necessitates the withdrawal of that portion of the latter's definition 

 of the genus with regard to the spines of the statoblast. 



Lophopus Lendenfeldii n. sp. is described, this being the first time the 

 genus has been recorded from Australia ; examples were also found in the 

 Paramatta river, New South Wales. The new species differs from L. crystal- 

 linus in the absence of the terminal spines to the statoblast, and in the 

 knobbed form of the inner end of the endocyst. 



Arthropoda. 



Simple Eyes in Arthropods.f — Mr. E. L. Mark is of opinion that 

 Mr. Locy's observations settle some of the disputed points regarding the 

 eyes of spider-like type. The formation of the retina from the epiblast, 

 independently of the cephalic ganglia, settles the controversy so far as its 

 hypodermal origin is in question. Some speculations are offered as to the 

 causes and the real significance of the hypodermal infolding which accom- 

 panies the formation of ocelli. The first difficulty is this : if the retina, 

 which is formed by a process of inversion, was once a normally located por- 

 tion of the hypodermis, how could it have remained functional during the 

 process of inversion ? and, in the next place, what led to that inversion ? 

 It may be assumed that the primitive eye was composed of a single layer of 

 modified hypodermal cells occupying the normal position (perpendicular) in 

 relation to the surface of the head ; that the proximal ends of the sensory 

 cells vp^ere in connection with the nervous centre by means of nerve-fibres, 

 and that the bacilli were formed in the distant or free ends of the cells. It 

 seems to be reasonable to suppose that all the triplostichous eyes have passed 

 through a condition of simple sac-like depression, in which the retinal cells 

 were not originally inverted. From this two conditions have arisen : (1) By 

 a closing together and fusion of the lips of the original depression a more 

 or less voluminous cavity (filled with a so-called lens) was formed in front 

 of the still uninverted retina, and behind a double layer of hypodermis : 

 such a triplostichous condition obtains in Penpafws. (2) By an approxima- 

 tion of the walls of the depression the cavity would be reduced to an axial 

 fissure ; the cells corresponding to the " outer cornea " in the first case 

 become the lentigen, those corresponding to the "inner cornea" become a 

 vitreous body, while the retina still remains uninverted : this is the condi- 

 tion described by Grenacher in Dytiscus. 



Two ways are suggested in which a change due to the action of the 

 light may have been brought about : one is that light gained access to some 

 portion of the periphery of the eye-bulb through other parts of the cuticula 

 than that which originally served for the transmission of light, and that 

 thus what was practically a new eye was developed out of a portion of the 

 already existing retinal cells ; to support this view we have the anterior 

 median eye in Agelena, which, very probably, previously existed in the 



* Journ. Linn. Soc. Lond., xx. (1887) pp. 61-4 (1 pL). 



t Bull. Mus. Comp, Zool. Camb., xiii. (1887) pp. 49-105 (5 pis.). 



