722 SUMMARY OF CURRENT RESEARCHES RELATING TO 



rare nuclei, or it has the ai^pcaraneo of a very delicate layer of proto- 

 plasui with scattcrcil uuclei. lu a word, the epithelium of the stomach 

 is as completely ditlercnt from an ordinary secreting epithelium as one 

 can well imagine, and this fact, in connection with tlu; diminution of tlio 

 lumen of the stomach as development advances, leads I\[r. Harnier to con- 

 sider the alimentary canal of Alcyonidium as a " rudimentary organ." 

 It is owing to the considerable amount of nutrient yolk in the egg, to 

 the fact that development is accomplished in the wall of the body of the 

 parent, to the extreme shortness of the free larval life, and to the degenera- 

 tion of many embryonic organs during metamorphosis that the ali- 

 mentary canal does not long preserve its functional form. 



The groove which aj^pears in the aboral region of the embryo, and 

 which has been regarded by Barrois and others as the jiallial cavity, has 

 probably the function of allowing the involution of the ciliary circlet 

 into the interior vestibule, which is formed during the process of fixation. 



With regard to tlic much dipcusscd pyriform organ, Mr. Ilarmer 

 states that it has, at first sight, the appearance of a mucous gland, owing 

 to the presence in its interior of a transparent substance which does 

 not stain easily. When examined more carefully, it is seen to bo 

 composed of a series of colls closely packed together at their outer 

 extremity, while on their inner side they are prolonged into fine pro- 

 cesses, among which are other cells full of vacuolated spaces. It is 

 important to note that there is no sharp limit between the pyriform 

 organ and the central mass of nerve fibres, which are prolonged into the 

 bases of the cells of the jiyriform organ. It may, therefore, be justly 

 supposed that the pyriform organ has a sensory function ; as the larva 

 ordinarily swims with this organ in front it is possible that its duty is 

 to test the bodies to which the larva desires to fix itself. It may be 

 noted that this organ has considerable resemblance to the cephalic shield 

 described by Kleinenberg in the larva of Lopadorhynchus. 



It is probable that the greater part of the nervous system arises from 

 the dorsal epiblast ; if this be so, the " brain " of Alcyonidium is the 

 homologue of the " dorsal organ " of entoproctous Bryozoa. On this 

 point the aiithor discusses the views of preceding writers, such as 

 Repiachofi" and Vigelius. 



It is probable that CypTionantes is not an archaic larva, but rather 

 one very much modified, in which the alimentary canal has preserved its 

 functional forms (owing, perhaps, to its larval life being longer than that 

 of other Bryozoa), while the oral surface is transformed into an atrium 

 in which the pyriform organ and sucker are situated. 



The descriptions given by Eepiachoif of the larva of BmcerhanJcta 

 cannot be easily brought into accord with Mr. Harmer's observations on 

 Alcyonidium, unless (as is probably the case) Repiachoff"s mantle-cavity 

 is really the internal sac or sucker, and the ciliated dorsal groove the 

 pyriform organ. 



Arthropoda. 



a. Insecta. 



Egg-membranes of Insects.*— Dr. E. Korschelt publishes a full 

 account of his researches on the formation of the egg-membranes, micro- 

 pyles, and chorionic appendages in Insects. The vitelline membrane 



* Nova Acta Acad. Cses. Leop.-Carol., li. (18S7) pp. 183-252 (.t pis.). 



