240 SUMMARY OF CURRENT RESEARCHES RELATING TO 



solid gastrula is also a syncytium, and tlie blastopore, until quite late in 

 development, is traversed by protoplasmic strands, wMcli anastomose 

 with similar strands projecting from tbe protoplasm lining the large 

 central vacuole or gut ; the gut arises as a vacuole in a multinucleated 

 mass of protoplasm. In describing the origin of the mesoderm, the 

 author states that at the commencement of the formation of the 

 somites the ovum is still a syncytium. 



Mr. Sedgwick points out that these facts explain, morphologically, 

 the connection between the nerve and muscles and sensory epithelial 

 cells, for the primitive continuity has never been broken ; there is 

 no essential difference between ducts with perforated cells and ducts 

 with so-called cellular walls. 



" If the protoplasm of the body is really a syncytium, and the 

 ovum until maturity in the ovary a part of that syncytium, the 

 separation of the generative products does not differ essentially from 

 the internal germination of a protozoon, and the inheritance by the 

 offspring of peculiarities first appearing in the parent, though not 

 explained, is rendered less mysterious, for the protoplasm of the 

 whole body being continuous, changes in the molecular constitution 

 of any part of it would naturally be expected to spread, in time, 

 through the whole mass." 



*' Shortly, these facts, if generally applicable, reduce the adult 

 body to a syncytium — to a multinucleated vacuolated j)rotoplasmic 

 mass, and embryonic development to a multiplication of nuclei and 

 a specialization of tracts in this mass." 



5. AracliiiicLa. 



Heart in Gamasidae.* — Prof. C. Claus describes the heart of the 

 Acaridse for the first time. It is best seen in the transparent larva of 

 Gamasus fucorum. It is placed in the posterior region of the body, and 

 consists of a single chamber with a slit-like valvate aperture on each 

 side ; anteriorly it gives off an aorta. It is thus similar to the heart 

 of Daplmia, and is probably degraded from a multilocular heart, such 

 as is found in the other Arachnoidea, just as that of Daphnia is 

 degraded amongst the Entomostraca. He considers Limulus and its 

 Palaeozoic allies to be more nearly related to the Arachnida than to 

 the Crustacea, and points out that the aerial respiration of the former 

 is not such a stumbling-block as some authors consider it, since 

 different forms may have taken to aerial respiration in different ways. 



Both the Crustacea and the Xiphosura, with the Gigantostraca, 

 have arisen from an ancestral Protostraca : amongst the Crustacea the 

 Nauplius-form and the doubled antennae persist, whilst in the second 

 group the anterior pair of antennae has disappeared, and other changes 

 have taken place. The third group of the Arthropoda Prof. Claus 

 regards as having arisen from some form like Peripatus. The characters 

 of the three sections — Sect. I. Crustacea ; Sect. II. Arachnida and 

 Gigantostraca; Sect. III. Peripatus, Hexapoda and Myriapoda — arc 

 given. 



* Anzeig. K. Akad. Wiss. Wien, 1885, pp. 250-3. Cf. Ann. and Mag. Nat. 

 Hist., xvii. (1885) pp. 168-70. 



