534 SUMMARY OF CURRENT RESEARCHES RELATING TO 



cannot be compared witli any known type of eye. In some, tlie 

 structureless lens is developed within the optic vesicle, and is a secre- 

 tion-product of the cells which compose it ; such eyes are to be found in 

 Gastropods, Cephalopods, Annelids, and in Peripatus. In others the 

 lens is developed outside the primary oj)tic vesicle, and is either 

 structureless as in many Arthropods, or composed of cells, as in the 

 dorsal eyes of OncMclium, and the eyes of Lamellibranchs, and Verte- 

 brates. The vestigial parietal eye of some Eeptiles appears to have the 

 same type of lens as the eyes of Charybdea^ for it is formed from the 

 outer wall of the optic vesicle. There appear, then, to be three types of 

 lens-eyes. 



Porifera. 

 Cliona.* — Dr. J. Leidy gives a short and interesting account of this 

 boring sponge, and describes a new form from the coast of Florida, 

 which he proposes to call G. pliallica ; it has an opening at its summit 

 which is closed when the sponge is disturbed. 



Protozoa. 



Functional Differentiations in Unicellular Beings.-j-— M. Fabre- 



Domergue replies to some criticisms of M. Maupas as to the existence of 

 functional differentiations in unicellular organisms. Taking Didinium 

 nasutum, he urges that at the moment when prey is ingested, there is a 

 clear axial tract, resulting from the formation of a canal which extends 

 from the mouth to the anus ; the existence of this canal is confirmed by 

 the retraction of its wall under the influence of iodine, and by the course 

 taken by the food which always goes straight from mouth to anus. M. 

 Maupas denies the existence of this canal because it has no proper 

 walls, but he likewise, it is true, denies that an air-bubble has walls. 

 Functional differentiation is still better marked in the excretory system ; 

 the most striking examjDle is the remarkable contractile plexus of Cyrto- 

 stomum, but it is only the most perfect expression of a structure which 

 exists in all Ciliata, and traces of which may be found in a large number 

 of forms. 



Maupas' Researches on Ciliata.| — Prof. A, Gruber does not accept 

 all the general conclusions which Maupas has drawn from his re- 

 searches on ciliated Infusorians. (1) The multiplication has been 

 shown to occur in asexual cycles, which end in degeneration and death 

 if conjugation does not take place. Therefore, Maupas maintains, the 

 doctrine of the immortality of the Protozoa must be abandoned. But 

 the conjugation always occurs in the natural conditions of life, so that 

 Maupas' objection is not after all serious. It is only necessary to add 

 to Weismann's original statement a saving clause as to the necessity of 

 conjugation. (2) Maupas opposes Weismann in regard to the equality 

 of the products of division. After 50-100 divisions the products are 

 both morphologically and physiologically different. But the species 

 still persists, and Weismann does not deny such variability, nor even the 

 inheritance of acquired characters in the Protozoa. (3) Maupas insists 

 that Weismann should have experimented before he theorized, but 



* Proc. Acad. Nat. Sci. Philad., 1889, pp. 70-5. 

 t Ann. de Microgr., ii. (1889) pp. 168-72. 

 X Uiol. Ccutralbl., ix. (1889) pp. 14-23. 



